Every race can choose between several primary Job Classes without requirements. Mastering a certain amount of action abilities for certain classes unlocks secondary jobs. Characters can freely switch to any primary or unlocked secondary class outside of battle.
All skillsets containing abilities the character has mastered can be equipped as secondary skillsets; the character will be able to use all mastered A-Abilities (action abilities) of this secondary skillset. Some abilities, like the Jump attack, additionally require certain equipment. The Item command is the default secondary skillset. Additionally, a character can equip all reaction, support and combo abilities they previously mastered in any class.
Classes not unlocked with any character won't be displayed on the class switching screen. Classes must be unlocked individually for each character. Unlocking a class for the first time will make that class option visible for all characters with compatible races, but they won't be able to use that class unless they meet the requirements themselves. Every time a character learns all the abilities of one job, that job will be marked with a star above it in the class switching screen.