How do you connect rooms and walkways to base?

[Tragic]

I am having a hard time working out how snapping works. Check this video... I'm trying to attach a room to a hallway, but I can not work it out.. only build it in space... I eventually get it, but I do not know "how" I got it.

https://www.youtube.com/watch?v=M5-9L_I21q8

TL;DR : How exactly do you "snap" objects onto your base.. is there a place I should be aiming the mouse for example?

[sweng]

Aim further from the connect point, it will become green and snap, connect it with some extra corridor automatically. Also turn the door direction with your mouse wheel to face to the connect point.

[Xaphnir]

Your issue was that at first it wasn't facing the right way. Once you rotated it 90 degrees and had it far enough away, that's when you got it.

Scanner rooms only have two connections, not 4, so if only sides without a connection are facing a connection, it won't connect.

[Grumpy-Granddad]

It will snap if close enough and at the right location.
You can also turn them if you are f.i. using the long tubes and such. You do not need to use the standard facing.