can you have sub jobs

So pretty much the headline is my question. Can you have sub jobs. So my charactor is a lancer. So can i at some point have him learn like magic spells or is all i can do is attack. Ive done a few duty finder jobs and seen others have both so how can i do that. Im slighty confused on the job system here. Someone please make this as dumb proof as possible please.

Each class has a set number of slots they can put abilities from other jobs into. The amount of slots is dependent on the level of the job you're currently playing. The abilities you can put into them depend on the job you're currently playing and the level of the job the ability comes from. For example, a character with the paladin job can use a slot to be able to cast the cure spell from the Conjurer job if the character has raised their Conjurer to a high enough level to have it. (I think conjurer's get it at level 2 but it's been forever and I don't remember, so if your Conjurer is only level 1 your Paladin can't use cure.) A Dragoon can't equip the Cure spell, even if the character has raised a conjurer high enough, because each job can only pick specific abilities from other specific jobs.