Watch this area for 'Recruitment' or 'Interest Check' threads. The GM will usually put up what he wants as far as submissions. Then create characters and backgrounds and submit to the recruitment. Then get selected, and have fun. :)
A few hints :
<Name of AP> threads. These are generally recruitment for that AP.
Threads with (closed) in the title. These are generally closed threads and are not accepting general submissions.
Threads with <System> in the title. These are generally threads for games in systems other than Pathfinder (For example, 5E, Champions, Shadowrun, etc).
Read this post. HERE