Kid,
The jig holds the recoil pad at the same angle as it would be on the stock, allowing the proper contour so it matches the gun when re-attached. You'll need a table-mounted disc or belt sander to use the jigs.
Try searching the Brownells website for particulars. You can even call their tech line for help before or after a purchase....they'll even help you if you don't buy their product.....good folks for sure.
Slim