Occupations are a type of job if you will, you can take. An occupation from what is currently known allows you to create all sorts of items, which mostly aid in helping regenerate an attribute of the player character. At any given time you can not take on more than two occupations and there is a three day cooldown before you can take another occupation. In the event that you drop an occupation the grade you had in that occupation will be lost.
There is only one trainer for each occupation. Each capital has only trainers for 2 occupations.