Whats the difference between cardio kickboxing, and MMA?

There's a HUGE difference. Cardio kickboxing is basically punching and kicking the air for fitness. It won't make you a good fighter. MMA is a training format where two or more martial arts are blended together. You learn to fight on the feet and on the ground. You'll get into better shape, but the sole purpose, unlike cardio kickboxing, isn't simply to exercise, it's to learn how to fight.