Im really lost :(

[Umo]

oh god, why the site of final fantasy is so confusing? it does not speak any of that

Yes, it does. More or less... At least for paladin, black mage and white mage

FINAL FANTASY x|v > ARMOURY > JOBS

By achieving sufficient mastery in a certain class, adventurers will be able to begin undertaking the mantle of a related job. For instance, gladiators may rise up as paladins, stout swordsmen who shield comrades from harm; thaumaturges may aspire to become black mages, masters of offensive magic; while conjurers may find a new calling as white mages, masters of healing.

PS. I do agree, the site does not offer proper/enough information on this. My nitpicking post is just to encourage you to read as much as you can in-game, active help windows and quests especially. Also, stick yourself to the main story quests and don't forget to go back to the guildmaster of your current class every 5 levels (5, 10, 15,...)