Because you want your colonists to use them.

You will want to use air-locks to section your star-base. Not only because it adds to the feeling of being in space, but because you will also want to vent the atmosphere from one section every now and then. For instance, when something catches fire. All air-vents are installed active, so when placing them on an outside wall, don't forget to shut them off!

Hint: Doors can be moved for free and safely. In Build menu, right-click doors to see other options.

Because it guides you through setting up your basic economy and introduces core game ideas.

You are an A.I. To you, these meat-bags are a cheap resource, easily regrown.

DNA is your resource for adding more colonists to your database, but growing them is for free. Therefore, it is useful to keep one colonist ready for growing in your vat as backup. Should your crew wipe, sit out the danger and grow the remaining colonist. It will collect your crew member's corpses (if possible) and you can regrow them for free - though death can cause a slight decrease in their learned skills. Poor meat-bags.

Buildings with a "+" in their icon can be right-clicked to show more options, like different walls, doors or beds. Also, when in building mode, you can freely select color in the bottom right corner.

Micromanage your colonists to pick up and put down items. Set the amount of items with the slider at the bottom of the pop-up window.

Crops don't want to be placed adjacent to walls. Other than that, they are pretty easily handled. But you may want to set them up in lines - makes it easier to use water-pumping for automation later.

Thanks to your toilets and tutorial, you know the whole line of producing nutrition bricks. Now use tanks and pipes to connect your facilities into a semi-automatic production line. (Biowaste itself must still be hauled.) Sell the bricks, eat bread and fancy food instead!

Starmancer introduces many features and mechanics which are innovative or re-mastered. For instance, by the time of writing this guide, broken turrets shoot your colonists. Not a bug, the security asset is broken and needs repair. Power it down first, though!

If in doubt, check the community hub and ask your questions or search for related topics. And don't hesitate to use the in-build bug reporting system from the ESC menu. It's fancy, quick to use, and helps the dev-team commit new updates!