Should Be Know Before Begin

First things, the guide uses a small amount of MMORPG terminology.
For those unfamiliar with the terms, here are some quick definitions:

Aggro
Used to refer to enemies who are aggressively attacking you.
An enemy wandering around minding its own business is neutral.
The second you get close and it starts attacking, you have "aggro'd" the monster.

Tank(ing)
The tank is a character whose main job is to take damage.
Having one person "tanking" can help quite a bit because you can give them a shield and cast spells like Protect and Regen.
If the monster can't bring down your tank, it won't be doing much to the rest of your party either.

Those are the two main terms. Here are a few others to throw around:
to "Buff" a character is to cast protective magic on him/her. Magic described as "AoE" is Area of Effect magic that hits multiple enemies in a specific area.
To "pull" a monster is the same as aggroing it. That about covers it.