Howdy, welcome to the boards!
If you're interested in a PbP game, you should head over
here, to the forum section called Welcome To The Shadows!
You'll see a bunch of various game threads, typically split into two kinds - In Character threads, and Out Of Character threads. If you're interested in joining a game, you should look for an OOC thread which lists itself as having Open Recruitment, then you should check the thread to see if the game roster is full. If you find a game that is openly recruiting and has open slots for players, contact the game's GM via Private Message.
Many games will be full, so try not to be discouraged. It doesn't hurt to contact the GM of a game that you're interested in and politely ask if they have any room and if you can be put on the list of "Reserve" players ready to jump into the campaign if one of the active players has to drop out for some reason. Just remember to be polite, and be willing to accept if they can't or won't accomodate you.
There is also a stickied thread at the top of that section of the forums, titled "
Sticky: Runners looking for a Johnson". Feel free to post a brief comment about what sort of game you're interested in playing and even what sort of character you'd like to play. GMs who are starting fresh campaigns will often check this thread and get in contact with people who have recently expressed interest in a game, so it's worth posting.
Remember, PBP is slow. Expect to not get into a game right away, and expect to have to wait for things even once you do get into one. PBP requires a lot of patience. Don't get discouraged!
Also, take the time to scan through most of the pages of a game thread - some GMs try to update the first page with relevant information, but it doesn't always happen. A game thread that looks full just from the first page might have recently had a slot open up, but you might only fight out about it on page 43 of the OOC thread or whatever. Also, it can help your odds of getting into a game immensely if you take the time to catch up on everything you weren't around for. Taking the time to read through an entire campaign shows that you're actually serious in your interest to play, and most GMs will appreciate that effort.
I hope that helps!
~Umi