When raising levels each player has 2 experience bars. First is his experience that is required to raise a level (LVL -1)*1000. A standard level does not give you feats, skills or new learned spells. In order to obtain those one must raise Sub-Class levels (LVL -1)*200. You may never have more than 1 sub-class level ahead of your actual Class level. 

Maximum Sub Classes - You may only raise 1 sub-class at a time and must declare which one you are raising. Explorers guild is the basic subclass and allows you to raise skill,spells and feats. If you choose to raise a different sub-class you must first exit the Explorers guild, although you may still work for them. Each Sub-class has a different way to gain EXP and may have requirements to be part of that class.

[Explorers Guild]

[Thieves Guild]