Well basically each race has 3 seperate classes. These 3 classes then branch of into 3 seperate classes. This keeps continuing till they've reached the final class. To gain a class u need level points. You can gain level points multiple ways: training, Missions(if they get added), arena matches and tourneys. It cost a certain number of LP's to get a class. I've made an example of what a human class would look like. It's preety rough so yea... Also these classes give you certain perks, i guess you can see from the image ill upload.
http://yfrog.com/1198097152j