Before you post anything! I do NOT want to know how to build a GOOD base. I just want to know how to build a base as in what the controls are.

And I have some other questions which would help me understand building a base better.
Can I undo what I've built?
Do I have to pick the brain body's weapons again after placing it?
How to keep the brain at the same place after I've used auto-base-building a few times when designing the base myself for once?
Why does the auto-base-builder keep my turrets where they were when taking over the site and not add new ones on top of or next to my base?
Why doesn't the auto-base-builder secure the parts of the base that were built by an enemy before I took over the site?

Building a base: When in construction mode, select bunker modules from the menu on the right and left click to place them into the world.
Undoing: nope, no undo.
Picking brainbot: Not sure what you're asking here. Every time you start a new map and select a brain char, it has no weapons, so you must always select weapons for it, if that's what you're asking.
Autobuild brain question: I don't have enough experience to say.
Turrets: The autobuilder is not intelligent, I've not used it so I can't give you a solid answer on this one either but I'm going to hazard a guess that it's too dumb to realize where to put more turrets.
Securing enemy bunkers: The autobuilder is not too smart. Don't trust it to do smart things like use pre-existing materials, if such exist, take advantage of them yourself in manual mode.

Picking brainbot: I mean that in a campaign, I'm defending an area and moved with the brainbot in the previous battle. When building the base myself after the battle, the game forces me to place the brain and pick its weapons again. This makes me waste hundreds of oz of gold.
For most of the other questions, thanks!
EDIT: I tried building the base myself and I realized that I only needed to pick another object to place.

I cam to give you an answer to this question!
Autobuild brain question: You have to do it manually, after the round starts :S Every, single, time.