Question

[Crowssoul]

Recently started and i'm getting up there in level now. But that means I am starting to think about jobs. From what i've found reading a couple wiki's is that even if i was to learn 5 other class (hypothetical) I could only learn a couple of the abilities.

Can someone clarify?

[Keydah]

I'm assuming off the wording you're talking about cross-class skills? If you aren't, ignore the rest of this.

The way it works is some but not all actions are cross-classable. When you don't have a soul stone (what turns you into your job at level 30), you can cross-class from any class's pool of cross-class skills. When you have your soul stone equipped, you can only pull from two classes that have abilities that fit it most.
For example, as an arcanist, you can cross-class flash from gladiator...there is no reason to EVER use it on arcanist (it purely generates aggro), but you need it when you play a marauder, so it's available from gladiator's cross-class pool. As a scholar (one of the arcanist jobs) you cannot use any gladiator cross-classes - you can pull from thaumaturge and conjurer only, because they have the most useful skills cross-classable. (stoneskin, cleric stance, and protect from conjurer, and swiftcast from thaumaturge)

Only actions that would be useful to other classes are available for cross-classing, so you can cross-class Physick to a Black Mage but not Shadow Flare (level 50 arcanist skill). Black Mage can also pull cross-classes from archer because archer has personal enmity-reducing (very very useful when you're nuking stuff for thousands of damage) & personal damage buffing abilities.

[Nutz]

You can only equip so many abilities at once (and only certain ones). For instance, you could level up archer, thaumaturge, conjurer, pugilist, and lancer to 30. At that point you could use any of those classes and equip 6 cross class skills (skills learned on another class). They're a bit restrictive though. When you go to equip cross class skills it only shows you the ones you can use.

At that point you can also complete quests to get soul gems (equip to change to a job). With that particular combination of classes you'd be able to change to Monk, Black Mage, and Bard. Jobs share abilities and traits with their base class (PGL -> MNK / THM -> BLM / ARC -> BRD), gain their own abilities through quests, and can assign cross class skills from only 2 other specific classes and only half as many abilities (so 3 at 30 -- 5 at 50).

I suppose it gets a bit complicated, but here are some links to get you sorted:
All job requirements
Skill trees

That second one lets you select a class or job to view all the skills it could use, what class they are learned from, and at what level.