The force is weak with this one. Your Google-fu needs practice:
http://www.dakkadakka.com/dakkaforum/posts/list/242387.page
Good of a place to start as any I have seen. With
GS (or any other sculpting), the best way to learn is to play with it. Although you can see how other people do things, you really can't get a feel for how it will actually work until you start working with it.
If you are looking at doing more complete sculpting, Ebob has a good introduction as well:
http://www.ebobminiatures.com/sculpting/sculpting.htm
Again, though - you really need to start working with it. Chances are pretty good that you will screw up the first dozen or so attempts at doing something, but that is a good thing. You learn by trying and failing.