Not exactly.

There are two seperate things you have to know first - classes and jobs.

A class is something that is more suited to solo battles (or small parties) and is much more customisable. When you reach certain levels with certain classes, you unlock jobs, much like in FFTA. For example, if you have a level 30 Gladiator and a level 15 Conjurer, you can unlock the Paladin job. A job is something that is much more suited to party play, being more specialist than the classes are. Note that the job is tied directly to the 'main' class that unlocked it - in this case, it's Gladiator. When I level up my Gladiator, I level up my Paladin, and vice versa. They share experience bars.

Regarding the levels of customisation...
Classes: On my L50 Gladiator, I automatically get access to every Gladiator action (ie, ability or spell). There are 15 of these. I can also use up to 10 different actions from other classes, too. So I could have 15 Gladiator skills, 5 Pugilist skills, 2 Marauder skills, and a skill each from Conjurer, Thaumaturge and Archer.
Jobs: On my L50 Paladin, I automatically get access to every Gladiator action. There are 15 of these. I can also unlock a further 5 Paladin actions. On top of this, I can also use up to 5 different actions from either Conjurer or Marauder (ie, I can not use Thaumaturge or Pugilist skills, etc).

Hope that makes sense. Any questions?