Here's a closer look at what the stats and skill/class window look like. (And also that Mage skill I mentioned earlier)
CP is used to learn class-specific skills (Magician). Money is used to learn class family (in this case, skills that are available regardless of which Magic-DPS class you are in) specific skills.
Each class also has their own unique innate ability - For Magicians, it's Cast Speed +5%, and M-ATK+10% (I think).
Certificates are gained for each class at certain levels (10, 20, etc.). The thing about Certs is that they carry over to any class you are at, so you can combine your certs to achieve your desired result! Using a combination of certain Certs also grants bonuses. The amount of certs you can equip at any one time depends on your Base level.
Lastly, Class Expertise! These are the "Passive Skills" of the game, if you will. Increasing Expertise uses up Knowledge points (1 for up to level 5, then 2), for a variety of effects, like M-ATK+1% per level, or Crit rate +2%.