Hey bud, its great to have you here, welcome to MMAF!
If you have any questions or concerns, don't be affraid to hit up a mod.
I suggest you try finding out what style of martial arts suits you best and start from there. Are you a striker or a grappler? But remember, the point of Mixed Martial Arts is to incorporate all(or most) styles into one.
The core styles for MMA are, Striking(Muay Thai/KickBoxing/Boxing), Grappling(Jiu-Jitsu/Judo/Sub-wrestling) and Wrestling(Greco-roman/Amateur/freestyle/Catch).
Other arts such as Tae Kwon Do, Karate or Kung Fu are used more as an accent to your style than anything else. So just remember to take your necessary deciplines and stay fit, because cardio is a BIG BIG factor in MMA.
Best of luck to ya!