First you go get the program here (
http://scummrev.mixnmojo.com/) . It has a decent help file and you can get information from the site, too, and there's a forum.
Basically, though, this is what you need to do. The program is kind of like Windows Explorer in that the contents of game files are represented in an expandable tree. In the case of GF music you'd just load up a music file (YearXmus.lab), expand the tree to see all the files, select tracks to preview or to save as WAV files. It's not a very complicated program. Once you've got WAV files you can edit them if you want (fading out the ends is a good idea on some), burn them to a CD, convert them to MP3, or whatever.