Well, when it comes to forums, as long as you know the gist of roleplaying, the rules (of sections and in general), and what the requirements are, you could hop into the OOC's of any new Rp going around in pretty much any forum (If you want, I can try to find an RP for you to start off with if ya tell me what you are looking for).
When it comes to starting off, either express interest in an interest check or create your character, put it in the OOC and wait for the GM to approve it.