I suggest Twinny's GS2 tutorial:
http://gs2.graalstudios.com/index.php?page=basic
There are also two tutorials on the Graal Bible, but I don't think they're as good. (One of them is a bit too quick to jump to the hard stuff, and the other I'm pretty sure no human could understand without having coded before)
You should also take a look at
Testbed Server. Partly because it's a good place to practice, and partly because there are other people there who are willing to help you out with stuff.