It is fun! And you're an awesome writer, so you should be great at it.
There's not a whole lot. Generally you need a summary of the RP's theme and story, its setting, and a description of races/classes/jobs, whatever is involved. Basically just compile enough information for the players to work from. Most that I've been in have required a profile of each player's character to be submitted before they'll be allowed to play, but the more casual ones just allow people to jump in and develop their character's personalities and backstories as they go along. If you'd like, I can link you to one or two of my old RP's as a reference.
im gonna fly off the handle
im gonna do some sort of acrobatic fucking PIROUETTE off the handle and win like a medal or some shit