Well, I assume you mean RSRP
An RPG is basically making up a story as you go along. With other people. You all create characters for the story, and then you post what the characters do.
All you have to do to join an "RPG" (Role-Playing Game - actually it's thread, but the name comes from the actual "games") is first find a thread - a story - to join and make a character to roleplay in that story. You can join one of the active RPGs (they're the ones that are stuck) or start a new RPG. (If you do, it won't be stuck, but I'll stick it as soon as I get here
To find out the idea of the story, or the rules of participation, look in the first post or if there's a discussion thread, read that.
If you're still confused let me know or ask Deac
, or Wraith 8
, or anyone whose name you see in an RPG thread in RSRP