Originally posted by GunsForBucks:

Walk up to workbench and "use" it. Key prompt should show when close to it. It will tell you if you need to cover it or not.

On the right side is the build menu. About three quarters of the way up is a hammer icon.
Click on that hammer icon until all your items are fixed. Repair is free.

Turns out that the prompt won't show up if you're equipped with the hammer. Found that little tidbit out by accident, and it would have saved me having to ask this, lol.

On another note. What does 'rested' actually do?