the crafting station that made the item also repairs it. Exception are the couple of items you can make without any station: those use the workbench to repair (a basic club for example).
its a little icon on the center of the left side of the interface to the crafting station.

your first crafting station is the workbench. There are other (?5? or so) crafting stations total that come along later.
you need 10 wood and a crafting hammer (build without anything, from a rock and a stick or two?) to make it. The bench needs a roof and walls around it so it isn't 'exposed' to function completely, but its existence will let you do the roof/walls basic building things. Once it has a roof, you can repair your club / axe/ craft hammer/etc.