Buildings are created with materials collected from your environment. A building site can be created by right clicking while holding the Hammer. Use the scroll wheel to rotate a building. Some buildings may only be created within water. In some cases, constructing a building will unlock more buildings. Increasing your skills in some cases can also unlock buildings. It is important to note that you do not need to have all the materials needed to construct a building in your rucksack when creating the build site.
To complete the construction building, you must right click the build site with your hammer. This will remove one of the needed build materials from your inventory and add it to the building.
You can find a listing of all buildings by clicking on the corresponding category link below.