Well you can always start off by reading, rating, and commenting on some of the stories on the site. The Price of Freedom: Innocence Lost is one of the newer big stories and a good place to start. Pretty much anything by EndMaster is a safe bet as well. Eternal is one of my favorites and I've heard great things about Rouges and Necromancer as well.
You could also play around with making your own story. If you want help with that I'd look around the Advanced Editor Forum, Writing Workshop, and maybe even the Creative Corner.
Lastly you could lurk around the forums a bit. There are plenty of good threads and good examples of how not to act, so it should help you in avoiding a ban.
Have fun and welcome to the community.