How do you select a second class?

[TuriousHD]

Oh sweet, thanks!

[TyloRime]

While the equipment sets are super helpful for keeping things organized, it is the swapping of mainhand weapons (and tools) that switch you from one class to another.

[Aleron]

Oh sweet, thanks!

Learning multiple classes is how you eventually unlock Jobs. Actually I found the system really confusing until someone explained Jobs are a bit like AD&D Prestige Classes. You need X levels of one class and Y of another and then you can unlock a super-specialized version of the main class. You can use fewer cross-class abilities, but you get big boosts to what you can do. In the end though, it means you don't end up with a Black Mage/White Mage, you end up with a really strong Black Mage with just a couple off-class abilities.