Buildings

Headquarters

The headquarters is where all recruiting of basic units and heroes occurs, and it also stores 50 food.  Without this building, you are effectively dead.

Farm

The farm is where crop weed is processed into edible food.  Buying and selling of food happens through here, and this is where basic units can be upgraded to farmers.  Finally, it also stores 50 food.

Silo

Silos are cheap food storage.  They store 50 food.

Tower

Towers shoot at enemies that come into range, and they do have very good range.  They have good damage and a lot of hit points, but are also very expensive, and don't hold up well against large numbers of enemies.

Barracks

This is where basic units can be upgraded to footmen.

Depot

This is where basic units can be upgraded to riflemen.

Chop Shop

This is where basic units can be upgraded to cavalry.