Prican Tex... are you a DO student or applying to DO school ?
OMM is a technique apply to treating the skeletal muscular system. It emphasizes strongly on system alignment whether you're doing HVLA, ME, CS, or FPR. Basically, if your body is in perfect working order, you should not feel any illness becuase your body can heal by itself.
i.e. if you have a herniated disc, thats the abnormality which will produce pain depending on which disc is herniated. Osteopaths can use OMM/OMT (both means the same thing basically) to treat the popped out disc through manipulation such as relaxing the muscles around the area and then treating with the techniques mentioned above for a set amount of time.
Another example, which I'm sure most of you have tried before, if you get cramps while exercising, what would you do ? stretch out your leg. Basically you're doing OMM to yourself on a more simple scale by not knowing it. You would further stretch out your muscles and they would relax in return and that would alleviate your pain after a few times.
I hope that further answers your question. OMM is NOT all about cracking and such, its about allowing your body to come to harmony with the rest of your functioning system. Goodluck.