[@PolkaDancer]

The website is a very individualized approach- joining an RP is decided by the GM. For the most part, you can join any RP partway through its story if the status says that they're still open, or you can sign up before it starts.

As for recommendations- you'll have to give your preferences for that. Science fiction? Fantasy? Slice of life? Realistic? Anime? Historical? Alternate Universe?