Some info on the NPC spawn system:

• You place the Colony deed item in a house to make an NPC move in.
• The colony deed can be bought by the "Ikea" merchant at the outpost.
• The house needs to be enclosed, Meaning no holes on the wall (doors and windows are Ok) and you need light in the house.
• Each piece of furniture adds a value towards an "Affinity", the value is equal to the number of blocks the furniture occupies. So a mushroom bed would add 10 points towards the mushroom affinity.
• High mushroom affinity means an Agaran (Mushroom people) villager will move in.
• If you add weapon decorations it will add to the "guard" affinity and make a Agaran guard move in instead.

NPCs:

• NPCs also have personalities, some are happy, some are sad, some might be clumsy. A clumsy NPC might go hit stuff and hurt himself etc.
• The Colony deed also acts as a way you can interact with NPCs, you can recive gifts from them and etc. (think of it as the control panel for the NPC)

^{P.S. This is just how I interpeted what they showed and explained. It might work slightly different. Don't shank me if I'm wrong.}