Dumb, stupid, idiot, moron, simpleton, smooth brain, potato head. These are words.

To build, you need to make a hammer. This can be done in inventory menu along with a couple other tools.

Once you make the hammer, equip it and Right-click and this will open the build menu.

You need to make a workbench, once you do you can use the hammer's build option so long as you are within the workbench's area of influence.

Then you need to sufficiently cover the workbench with walls and a roof. This will allow you to actually use the bench in order to repair and make new tools.