Hello again. Well, sure you can join. We currently have two RP's going. One that I run (kinda) and coolmike's.
Well, RP's are kinda like writing a story, except you only write the part for your character. You can't control another character's actions. If I'm playing Leo (which I am) I'd have him walk into a room and say something to say, Raph. Then I'd have to wait for Raph's player to respond and so on. Kinda like a Round Robin. You can follow along with the TMNT RPG chapter 4 and get the idea.
Most of the main TMNT characters are taken so, yes, you can create your own character, and yes it can be a Turtle. Just post your character profile in this thread:
http://www.thetechnodrome.com/forums...forum=4&84
There are a few examples already there. You don't have to tell us more than you want.
I hope that answered your questions. In the very least I hope you didn't end up even more confused. Feel free to ask about anything else.