First things' first, you gotta figure out what you like. For example, I like giant robots and post apocalypticness and such like that. Second, you determine your own skill level. I'd go for either 'free' or 'casual', for a newb such as yourself. Go to the relevant sub-forums (
http://www.roleplayerguild.com/forums/3-free-roleplay < free
http://www.roleplayerguild.com/forums/4-casual-roleplay < casual), and just snoop around the available RP's. Find one you dig, then usually you're gonna need to fill out a few forms, here they're known as '(Whatever) sheets',but usually, 'Character sheets', although in the nation-RPs they're Nation Sheets, for example. Anyway, you basically say you're interested in the thread, make a post, and put a filled-out CS (should be found in the OP of that thread) inside a hider in your post.
More or less, as long as you think things through thoroughly, you should be peachy-keen fam.