Brand new to this
Happy to help!
In a nutshell, play is run through individual games, each of which has their own set of boards and threads which form the basis of play - how they are structured tends to be up to the whim of the GM, who owns that particular game, sets the rules and enforces the policies.
If you want to join an existing game, they advertise on the Wanted - Players thread, on which you can update and get bumped to the top of the list once a week, so it's worth waiting to see if something comes up on the cycle if it's not immediately obvious.
Alternatively, you can ask for a GM to run a particular type of game on the Wanted - GMs thread, or set one up on your own.
When you're asking to be added to a game, it's known as an RTJ (Request to Join) - you click the 'request access' button in the top right hand of the game's forum page and it'll allow you to send a private message to the GM to alert them that there's someone interested, and they can then begin the discussion with you about fitting you into the games.
As long as a game is taking players, most GMs should be happy to have those conversations and try and fit you in, but ultimately it's their decision and they may be balancing other things, so if someone says no, don't take it personally and just look for the next game.
Aside from that, make sure you read through the FAQs (top right hand of every screen) and familiarise yourself with the rules, especially ADULT and Mature policies, because that's something that's obviously quite important on a site like this.
Aside from that, be nice and we'll all get on fine!