In FFXIV you have 2 levels associated with your character(ffxiv gil): Physical Level and Discipline (class) Level. The physical level (also referred to as Rank) will continuously increase no matter what discipline you are playing. This means if you are play a Marauder up to level 3, and switch to a level 1 Conjurer, your physical level will remain the same. Also, each rank you gain from your physical level gives you attribute points you can assign to the various stats associated to your character, as seen in the image above. Right now you get 70+ attribute points per rank to assign to your various stats. The cost of a stat will increase as you point more and more points into it. We have a basic simulator for stat point allocation (it's a work in progress).
Your Discipline Level dictates what abilities you have access to. So as a level 1 Conjurer you'll have access to some basic attack spells, at level 2 they get an ability called Trance Chant. Now lets say you switch to Marauder, your physical level will remain the same, but your discipline level is now level 1. When you hit level 2 with Maruader, the level 2 Chanter spell is available for the marauder to equip. Some abilities have restrictions (like a Marauder ability will say "Marauder only", or it could say "Discipline of War only" or "Disciplines of War and Magic only". As well, when equipping an non-main spec ability (a Marauder equipping a casters "cure" spell) it may have higher cast times, cooldowns or cost. For example, if you look at the image below, "Trance Chant" has a 120 second cooldown when a Marauder equips it. This same ability has no cooldown when a Conjurer equips it. Notice that this is a level 2 axe (marauder) with a Conjurer spell equipped.
