It's tab writing software, I use it to learn songs though. You can search for and download tabs from the web into GP. When you open the song in GP, you get the notation, the tab on the screen and the sounds with a mixer so you can take the bass out or boost it etc. You can loop sections, slow 'em down etc. A marker moves along with the tab so you know where you are.
It's the dogs bollox and worth every penny