Building is a crucial part in the mechanics, the NPCs that unlock many of the features in the game and needs to be provided accommodations to help you achieve your goals. When a building is complete NPCs can be placed into it to make them a part of your society. Many mechanics such as the weapons crafting, items crafting, talents crafting and more requires a talented NPC to be present in your town who is willing to work for you.
Each NPC has their own requirements to stay in a house. An NPC who is proficient in a field will need accommodations to support his/her talents. For example blacksmiths requires at least an anvil to be present in their room. As you put in more tools for them to work with, the number of items they can craft increases. Each room in a building is reserved for new comers and you will be able to place a refugee into one. Not all of them will be content though, some refugees might be looking for a more luxurious place to stay while others are content with 4 walls.
Buildings in Crisential can be placed brick by brick. Constructing a building is done by two steps. The placement of the building and the construction itself. In the Building mode, you can place walls, doors, stairs and windows to shape the building itself. After you designed the building you can place items in it depending on what type of NPC you want in that building. Each building can have multiple NPCs in them provided they each have their own rooms and the rooms meet the requirements of the NPC.
The second step is the construction. This can be either done by yourself, or with the help of your construction worker NPCs. The assigned NPCs will continue build the society even if you are off at the wastelands doing something else.