First, make sure you have the multitool up. Bring it up with ctrl+r.
Take off what you want to repair. Make sure you have the repair tab clicked. It asks you for the slot number of the item. Enter that into the box and click the repair button.
Ex: You want to repair a hat. Un-equip the hat so that it goes into your inventory. Now going from top to bottom, left to right, enter in the slot number of the hat. My hat went into slot number 1 because I had nothing else in my inventory. Enter the number 1 into the box. Click the repair button. Re-equip the hat.
Side note: Make sure you have enough money on you to repair, because it still costs gold.
As far as downloading, extracting, w/e to get it to work properly, read the thread from the link I gave you in my previous post and it will explain all of that. :)