This site is pretty straight forward (and I think you'll enjoy it). There's 3 kinds of main group RP's.
Free, which is kind of the E for Easy going RP's. Casual, which has a fair amount of writing but not strict. And Advanced, which has a good amount of writing and for people who have been writing/role playing for awhile. Then there are the Nation RP's which have you making continents and governments and countries to RP with in a storytelling/strategy mixture. And there is 1x1 if you just want you and a partner. And then there is the Tabletop like regular D&D, and finally the Arena for combat RP's.

Ok, if you want to join/make an RP. Here is usually the layout. The "Interest Checks" are for people to post their RP ideas. Then when they have a fair amount of players, they create the threads that are located up in Free, Casual, Advanced, etc. Those threads are split up into IC (in character, for actual RP postins), OOC (out of character, to discuss ideas and say you are interested in joining) and CS (character sheets, where you post finished characters).