Trying to find my way around
Heya, welcome to RPOL :). If you're looking to join a game you can check out the "Wanted - Players" subforum, or alternatively there's "Wanted - GMs" if you're looking to run something.
Generally people will post up a game they want to run and then people apply to join by sending a "Request to Join" (RtJ) which tends to contain your character concept and stuff like that - different GMs ask for different things so it's best to check in the game first (there's usually a public thread there with such info) and make sure you submit what's being asked for :). If a GM is interested then hopefully they'll reply and you can get yourself into a game. There is a wide range of systems being used here and feel free to post up and ask about any you want to play in, even if you don't see them here (some systems are more popular than others, like DnD for example).
There's also the FAQ and Help functions (see the very top-right corner of the screen) which should also give you a bunch of general info on anything general you might want to ask about regarding how the site works :). It might also be possible to ask to lurk in an existing game (which lets you read but not write posts) if you want to get a feel for how things work, though bear in mind every game is different - within each game, it's solely down to however that particular GM wants to run it so what's true in one game may not be so in another.
Anyway, enjoy your stay and have fun, find some games and get playing :D.