Ok, I've been having a TON of fun with this game. It's what I had wished Minecraft had been. The building in Minecraft was fun, but it lacked any sort of adventure.
bansama: I'm still trying to figure out how to build a house =/
Don't use dirt for the walls or ceiling, and you need to replace the background with a crafted material (wood/stone) that you make with the crafting table in order to keep monsters from spawning in the house.
Other than that, what specifically are you having issues with?
Detlik: Why the npc wont stay in wooden house?
What do you mean by won't stay in the house? They don't stay put, they wander around a bit.
But, they will stay in the close proximity to their home/room.
The guide will eventually move into the first house/room you build (You'll need 6 rooms for all the current NPC's).