When you first start a save in Caves of Lore, you select which trait you want to start with. There are two categories of traits when starting the game:

• Weapon Proficiency Traits
  
• Spell Proficiency Traits

Your starting character will have a blade, so if you want to deal some extra damage early on, selecting blade proficiency is a pretty good option. It is worth considering that often you will switch the weapons on your characters use often in the early game so you may want to wait until later to select a weapon proficiency if you are playing conservatively. However, Caves of Lore gives out trait points quite often, so I wouldn't stress it too much.
If you chose to start with a spell proficiency, I would recommend choosing Agent of Destruction. Most of the spells that you will focus on are in the destruction class because those do the heavy damage. Since you will use them a lot, it's good to get some extra damage onto those.

Throughout the game, you will be able to obtain several new traits. Every 3 levels (when you level up to a level divisible by 3), you will gain a trait point. A trait point can be used to obtain new traits

When you have at least one trait point on a character, there will be a blue circle next to the character and in the inventory the traits tab will be highlighted blue.
When you click on the traits tab you will see the list of traits that you have on the character, you can navigate them using the arrow buttons and read their descriptions. At the bottom, you will see a box with a blue number in it showing how many trait points you have available.
Clicking the buy traits button next to it will allow you to pick a trait to unlock and clicking the "buy" button while a trait is selected will purchase that trait.

In Caves of Lore there are several traits that are locked and are unable to be bought.
You are not able to read the descriptions for these traits, so the only way to learn about them is to unlock them.

The way you unlock these traits isn't super obvious but once it is pointed out, it is very simple.

If you click on your Codex and select the "Monster Lore" button, you will see information about each of the enemies you've encountered.
Many of the monsters in this book will not have their strengths and weaknesses available, there are progress bars for each piece of information that progresses by fighting that monster enough times and is greatly effected by the "monster lore" skill. At the bottom, there is a "lore bonus" that is locked. Once enough information about that monster is learned, the lore bonus will unlock which will allow you to acquire the associated trait.
The lore bonus can also give you additional damage against that monster so it is very valuable to learn the lore about the enemies in Caves of Lore.

The Monster Lore skill is incredibly valuable in this game and it is suggested to dump a lot of skill points into it. When calculating monster lore, the game will add up the Monster Lore skill of your entire party.
The monster lore skill is also modified by your MIND level.