All characters start out as Novices, with a Base Level and Job Level of 1. Once they reach job level 10 they can choose between a variety of first job classes.
If choosing one of the standard first jobs, once they then reach at least Job Level 40 (up to a maximum job level of 50) they can then change to a second class job, picking from two possible choices for each first class.
Then after reaching Base Level 70 and Job Level 40 as a second class they can choose to advance their class to 3rd Job.