Hey Kick it's pretty easy to use. Purchase the decal paper from ebay. Print your image or logo onto the paper with an inkjet or laser jet printer. Let it dry for a few hours. Seal the logo/image with a clear coat. Let dry overnight. Cut as close to the image/logo as you can. Submerse it in water for a few minutes then the backing paper will peel off. Place the logo on the guitar. Apply more clear coats for protection
The good thing with the laserjet decal paper is you don't need to do the sealing coat - but you certainly need to with the inkjet one!