Well. MMA is something different from TKD, or Karate ,or Boxing.It has actually a huge difference from one to the other. MMA contains the use of almost every muscle in your body and of-course u;ll need to do some weight training , because u need to built your upper body as well in MMA.
u'll have to do something more than push-ups.
However, u can start at least by doing, 3 set, OF 20 push-ups, For-let me think-,3 round every day for at least 1-2 weeks before going seriously for it.
It's not that hard.It's just that it is another class from what u were doing soo far.
Have fun and try your best men.