You do not get to choose what classes you go. Instead, they are determined for you through some external force. If not otherwise specified by the GM, this is determined randomly. However, you get your first rank at level 1 instead of level 6. You are still proficient in the abilities you get through this rank. This extra rank does not give you additional hit dice, mana dice, HP, or MP.
Once a class is determined, you stick with it for two ranks. After that, you will start learning a new class and stick with it for another two ranks. It is possible to get the same class for multiple sets of two ranks.
Every two ranks, you gain an additional flaw as well from the following list.