As mentioned above, it's the weapon or tool you equip that actually determines your current class, but with different classes needing different armour/jewelry (both because of being different levels and because of gear designed for a particular type of class/job), you'll usually want to swap out all your gear at once when changing classes rather than just your main hand weapon/tool. To make this easier, the game lets you assign gear into Gear Sets, so instead of just equipping your saw, for instance, you'd equip your Carpenter Gear Set, which would include your saw and whichever armour and jewelry suits a crafting class at your current CRP level.

This sounds awesome. . .will I get a pop up tutorial explaining how to use and set up gear sets?