Within the game there are two important types of buildings. Facilities and complexes (sometimes known as hubs).
There are many facilities and complexes in SRCW with a wide range of uses. They all require Industrial goods to build. Some require Military Goods as well.
Both types are built within a hex and each hex can hold a maximum of 1 complex and 6 facilities.
Complexes are the center, or base, of a hex and one must be present before other facilities can be built on a hex. Different types of complex have different uses. Most complexes enable construction of similar types of facilities and do not allow other types of facilities. For example a military complex will allow military facilities to be built around it, but not industrial facilities.
It should be noted that, because of the overlay of categories for some types of facilities this is not a universal rule. For example military goods facilities can be built on both an industrial and military complex.
Also civilian population centers, towns etc, act as a type of complex and can hold a wide range of facilities.
Facilities are the backbone of your economy and range in type from factories to power plants, fortifications to airfields. Which facilities can be built depends on what type of complex is present and what type of facility you wish to construct, as well as the available resources on the hex.
Industrial Facilities are for Harvesting or creating resources. Everything from farms to power plants
Civilian Facilities are facilities that fall into another category but can be built in Cities and towns as well. Most Industrial facilities and some military facilities fall into this category as well.
Primarily used for the creation, repair and storage of military units these facilities are important defending a nation. Other types of military facilities include Air defense sites and radar stations.