What's up guys, Sergeant Conagher here, with a guide. This guide is for players who have no clue how to play Engineer. I hope new players can understand this, so let's get to it!
There will be a lot of text ahead, but reading this guide to completion should help you fully understand what an Engineer does.

The Engineer's main role is to construct buildings like a Sentry Gun, a Dispenser and 2 Teleporters (1 exit and 1 entrance).
Let's start with what you see just by picking the class: 125hp, a Shotgun, a Pistol, a Wrench, the number 200, four boxes with strange images and a PDA.
You have the same HP (hit points) as a Scout or a Sniper. Unlike a Scout or a Sniper, the weapons you have are not very powerful. As an Engineer, your buildings are your main weapons.
The PDA is used to construct buildings, which you will learn about in a bit.
Those four boxes show your buildings' status. You will be able to see how your buildings are doing in terms of ammo and health.
Remember the number 200? This number is your Metal count. It is what you use to build buildings, upgrade them or repair them.

Buildings:
Sentry Gun:

This will be your main damage output, and is extremely effective for defending an objective. It shoots at all enemy players in its range (The team-coloured bubble you see when you are about to build a Sentry is its range). Every bullet fired by your Sentry Gun will deal 16 damage, and fires 4 bullets every second.








Dispenser:

This will supply health and ammo to teammates. It also generates metal to use.


















Teleporters:

This will do as the name says: teleport teammates. The Teleporters are simple: step on the Entrance, teleport to the Exit. Teleporters have a 10 second cooldown after a teammate is teleported.











Basics for buildings:
To construct a building, select your Construction PDA.
1, by default, selects the Sentry Gun, 2 selects the Dispenser, 3 selects the Teleporter Entrance and 4 selects the Teleporter Exit. Next to the image of the buildings are numbers. These are the metal costs for each building. Sentry Guns cost 130 metal, Dispensers cost 100 metal and both the Entrance and Exit Teleporters cost 50 metal each. To destroy a building, select your Destruction PDA (The one with the antenna and the big red button), and press the same key you pressed to build the building initially to destroy it.
When a building is selected, the Engineer will be shown holding a toolbox, and a blueprint will appear in front of you. This blueprint will show you where your building will go. While this blueprint is shown, you can right-click to rotate the building by 90 degrees. When you left-click, the building will begin construction. While a building is constructing, you can hit it with your Wrench to speed up the initial construction process.

All of your buildings can be moved by walking next to them and right-clicking them. You can then take your building to wherever it is needed. You can left-click to put your building back down. This is called " Hauling". You can only haul one building at a time. You also move slower while hauling, and you can't switch weapons. If you are killed while hauling a building, the building you were hauling is destroyed.
























Buildings can also be upgraded to increase their effectiveness. All buildings can be upgraded up to Level 3, at a cost of 200 metal per upgrade. To upgrade, you need to hit your building with your Wrench until it upgrades. Every hit with your Wrench spends 25 metal when upgrading. It is of note that during setup time, this number is doubled, making building setup during setup time a lot easier.

Upgrading your Sentry Gun will double its rate of fire at Level 2,
















and will be able to shoot rockets every 4 seconds at Level 3.



















Dispensers get an increased heal and ammo replenishing rate when upgraded. They also produce more metal at a time when they are upgraded.

Teleporters have a decreased recharge time when upgraded. A 5 second cooldown at Level 2, and a 3 second cooldown at Level 3.
Every Level 1 building has 150HP, every Level 2 building has 180HP and every Level 3 building has 216HP.
If your buildings are hurt, you can hit them with your Wrench, at the cost of some metal. The health to metal ratio is 3:1. However, you can only spend a maximum of 34 metal per swing, healing 102 damage. You can also refill ammo from Sentries by hitting them with your Wrench, also costing some metal. Bullets have a ratio of 1:1 and Rockets on Level 3 Sentries have a ratio of 1:2. Like healing, you can only spend 56 metal per swing, replenishing a maximum of 40 bullets and 16 rockets. You will only spend 90 metal maximum per swing with all of these things combined on a Level 3 Sentry, replenishing health and ammo for both bullets and rockets. Every other building will only consume 74 metal per swing.

There is an order to how metal is spent on buildings:
1)Health
2)Upgrade Progress
3) a. Bullets
3) b. Rockets

You can only pool your metal in two of these at once. Whenever a Sentry is upgraded, its ammo reserve is fully replenished.

How to be effective: There is a reason why the Engineer is considered a defensive class. He defends, and he's darn good at it. He isn't a class that is normally very aggressive. A smart Engineer should stand by their buildings, but also watching out for their own life.

You should also know when to play Engineer. If there are 2 or more Engineers on your team, your best option is to not play Engineer. Also, since the Engineer is considered a defensive class, you should normally not play as him when on Offense on Payload, Attack/Defend maps, and most King Of The Hill maps. Playing as an Engineer on Capture The Flag, Special Delivery, when on Defence on Attack/Defend and Payload or when when defense is needed at your Control Point in Control Points is a good idea. Engineers on Payload Race are not very helpful.

The choice of map can also change when you should play as Engineer. You have to understand when your team needs a defense and when it doesn't and can hold it's own.

Remember the name of the game: TEAM Fortress 2. The best thing to do is to play with your team in mind. Engineer's best friend can be a friendly Pyro, as he has a Flamethrower which can be used an effective Spy-Checker and he has weapons like the Homewrecker and the Neon Annihilator.

Your biggest weaknesses:
Spies:
The Spy has a tool which is made to disable and destroy your buildings, the Sapper. If one of your buildings has a Sapper on it, it will disable it and slowly lose health before being destroyed. Although removing a Sapper is easy: hit the Sapped building with your wrench twice and BOOM, the Sapper is removed. Sappers also affect both the Entrance and the Exit Teleporters, however they can be removed from both on either side.




Enemy Spies can also use Teleporters built by your team, so watch out. Staying on top of a functional Teleporter could kill you or any teammates also staying on top of it, if a Spy decides to take the Teleporter. This is called a "Telefrag".











Über:
Über is an ability used by the Medic, obtained by healing enough teammates. Über usually used to push though an area that is much more difficult to push through normally, since it creates a powerful effect, being invulnerability, extra damage, fast healing or damage protection. Unfortunately for Engineers, a well-placed Sentry Gun is a big target for an Über. So, don't feel so bad when an Über rolls through your base. When an enemy Über is used, be ready to Haul your buildings away.









Being outranged: As previously mentioned, your Sentry Gun has a limited range. Most classes can stand at a fair distance away and take out your buildings. To prevent this, watch the range of a Sentry Gun and try to place it where it can't be easily taken out.

Let's talk weapons of the Engineer.
The Engineer has 11 unlockable weapons to chose from, so let's take a look at his arsenal. Please note that unlockable weapons change often, and this guide will be hopefully be updated when any weapons are changed.
Some weapons can be earned by getting a certain number of Engineer acheivements. I will put the number of acheivements required to get an item in it's description.
You can get any weapon through the Item Drop system, which resets every week, and allows you to find 3-12 items per week. Some may be Engineer weapons, but most are for other classes. To see what class the weapon you found is for, there should be a picture of the class it is for. There are some exceptions to this rule.

NOTE: Any italicized stats are not present in the weapon's description in-game but are a part of the weapon (hidden stats).
Primaries:

Frontier Justice

Stats:
Gain 2 revenge crits for each sentry kill and 1 for each sentry assist when your sentry is destroyed
Revenge crits are lost after death
-50% clip size
No random critical hits

What can this be used for?
This gun is perfect for new Engineers who have their Sentry Guns being constantly getting taken out, while still getting some kills on it. Its has 3 shots instead of 6, so you will be reloading more often.

You can unlock the Frontier Justice by getting 5 Engineer achievements.

Widowmaker

Stats:
On Hit: damage dealt is returned as ammo
No reload necessary
10% increased damage to your sentry's target
Uses metal for ammo
Per Shot: -30 ammo

What can this be used for?
Because you gain metal from hitting enemy players, if you get a lot of good shots, you can gain metal for buildings, and since you don't need to reload, you can keep shooting forever, if your shots are well-aimed. The extra damage when you shoot at your Sentry's target is nice, but don't rely on it to get kills that you wouldn't normally.

Pomson 6000

Stats:
Fires energy beams instead of shotgun pellets
Does not require ammo
Projectile cannot be deflected
On Hit: Victim loses up to 10% Medigun charge based on range
On Hit: Victim loses up to 20% cloak based on range
Deals only 20% damage to buildings
-34% clip size
-20% damage ramp-up
-28% slower firing speed

What can this be used for?
This gun is perfect for countering the biggest weaknesses of an Engineer, the Spy and Über, however doesn't really succeed at doing anything else sadly.

Rescue Ranger

Stats:
Alt-Fire: Use 100 metal to pick your targeted building from long range
Fires a special bolt that can repair friendly buildings for up 60hp per bolt
Bolts heal at 4 heath per 1 metal
-50% max primary ammo on wearer
Self mark for death when hauling buildings

What can this be used for?
This gun allows you to be more mobile while keeping your buildings alive from a distance. If your Sentry is being targeted by, say a Heavy, you can back off into a corner and hopefully keep the gun alive by shooting at it if you have metal. If an Über rolls in on your buildings, you can teleport them to you for 100 metal each. It does have less ammo than the Shotgun, so you'll have to watch your ammo. Also, the bolts that the Rescue Ranger shoots don't do much damage, so being aggressive with this gun is not recommended.

Panic Attack

Stats:
+50% bullets per shot
This weapon deploys 50% faster
Fires in a fixed shot spread
-20% damage penalty
Successive shots become less accurate

What can this be used for?
The Panic Attack is best used when you want to go full offensive. However, as previously stated, Engineers should usually never be offensive. This gun better suits a Killing Gloves of Boxing Heavy than an offensive Engineer, however it can be effective for Engineer.

Secondaries:

Wrangler





Stats:
Upon deploy, take manual control of your Sentry Gun.
Press Fire to fire your wrangled Sentry Gun's bullets.
Press Alt-Fire to fire your wrangled Sentry Gun's rockets.
Wrangled Sentry Guns have +100% faster firing speed.
Wrangled Sentry Guns gain a shield that reduces damage and repair rate by 66%.
Sentry Guns are disabled for 3 seconds after becoming unwrangled.

What can this be used for?
This weapon allows your Sentry Gun to shoot at any range, but is manually controlled. If you get taken out while your Wrangler is out, your Sentry Gun is disabled, however keeping its shield with a massive 66% reduction in damage.

You can unlock the Wrangler by getting 17 Engineer achievements.

Short Circuit





Stats:
Alt-Fire: Launches a medium-range projectile-consuming energy ball
No reload necessary
No random critical hits
Uses metal for ammo
Per Shot: -5 ammo
Per Alt-Fire Shot: -65 ammo
Primary fire deals only 20% damage to buildings

What can this be used for?
This weapon allows you to negate Soldier and Demoman explosives with the click of a button. It does not have insane damage, so this is not an aggressive weapon, when it come to direct damage.

Melees:

Jag





Stats:
Construction hit speed boost increased by 30%
+15% faster firing speed
20% slower repair rate
-25% damage penalty vs players
-33% damage penalty vs buildings

What can this be used for?
This Wrench is perfect for building a base fast, with its faster construction rate and swing speed. Keeping the base alive is another story entirely. Because of that slower repair rate, and -33% damage to buildings, i.e. Sappers (yes, they are considered a building), it is harder to keep the base alive. Still not a bad Wrench though.

Southern Hospitality





Stats:
On Hit: Bleed for 5 seconds
No random critical hits
20% fire damage vulnerability on wearer

What can this be used for?
This is the ultimate of Spy counters. Since it makes enemies bleed, it is much easier to find and kill the sneakiest of spies.

Eureka Effect





Stats:
Press your reload key to choose to teleport to spawn or your exit teleporter
-50% metal cost when constructing or upgrading your teleporters
Construction hit speed boost decreased by 50%
20% less metal from pickups and dispensers (including Payload carts)

What can this be used for?
This Wrench allows for a more supportive role. Since Teleporters cost 25 metal to build and 100 to upgrade, 200 metal can get your Teleporters built and upgraded to Level 2 with 50 metal left. Just be cautious of your metal supply.

Gunslinger





Stats:
+25 max health on wearer
Sentry build speed increased by 150%
Third successful punch in a row is always a critical hit (3x base damage)
No random critical hits
Replaces the Sentry with a Mini-Sentry

What can this be used for?
Remember when I said that Engineers should not be offensive? Well, this lets you become one. With an extra 25HP, you can do more aggressive things as an Engineer. Also, your Sentry Gun is replaced by a Mini-Sentry.

Here are the Mini Sentry's stats:
-30 Sentry build cost
+50% faster Sentry firing speed
+35% faster Sentry rotation speed
+150% faster Sentry construction speed
Starts at 50% max health when placed and slowly builds health up to 100% while initially constructing
-50 max Sentry health
-50% Sentry damage penalty
Cannot be upgraded
Destroyed Sentry parts yield no Metal

What can this be used for?
The best use for the Mini-Sentry is to go full offensive. It is smaller, allowing for more aggressive spots to arise. Just remember that it is easily taken out.

You can unlock the Gunslinger by getting 11 Engineer achievements.

Combat Engineer:
Frontier Justice
Pistol
Gunslinger





Why put these weapons together?
Because your Sentry will be destroyed quickly, if it gets a couple of kills, it will help your Frontier Justice. Your pistol is there in case you need to shoot back and your Frontier Justice is out of shots and needs to be reloaded.


Anti-Spy:
Pomson 6000
Short Circuit
Southern Hospitality





Why put these weapons together?
Your Pomson 6000 will help in removing cloak from spies, and your Short Circuit and Southern Hospitality will aid in tracking down invisible spies.


Dug-In defense, yet still a little mobile:
Rescue Ranger
Wrangler
Jag





Why put these weapons together?
The Rescue Ranger is good for those situations where reparing a Sentry with your Wrench is not a smart idea. You can stand back and continue to heal your Sentry. Your Wrangler is good for getting that one enemy who is just out of your range, or who is quickly peeking at the Sentry. Your Jag helps in getting your base built fast. If you need to move up quickly, the Rescue Ranger has you covered.

Engineer can be a difficult class to master, however this guide will have helped you get started in your Engineering indevers. I hope this will help you become better as an Engineer.