Professions
Now lets talk about making money. Doing quests and stuff can give you a little bit of cash in game, but not a lot. So you're going to need jobs. There are two types of professions; Primary and Secondary. You are only allowed to take two Primary professions, but you can take all Secondary professions. The Primary ones will be your main money makers.
Inscription - Create glyphs and scrolls that enhance abilities and spells.
Jewelcrafting - Craft rings, necklaces, trinkets, and all kinds of powerful gems to add enhancements to armor and weapons.
Leatherworking - Work leathers and hides into leather armor.To start out you will want gathering professions (herbalism, mining, and skinning). Most herbs and metals will sell for a lot on the auction house and this is a good way to earn some money. Cloth will also sell for quite a bit.
You can also pay to change your professions later, after you've made a good bit of money. Engineering is not a good starter profession as you will end up spending more than you make just to create stuff and level your profession.
Each class has three different talent builds to choose from that will determine what spells and abilities they have access too. For example, a mages talent builds are Frost, Fire, and Arcane. A priests are Holy, Discipline, and Shadow. And a warriors are Arms, Fury, and Protection.
As you level up you will gain points (though apparently very few of them) to place in your talent trees. When you place a point in a spell, you can learn that ability.
You can also pay to duel spec, meaning you can have two talent builds at once. For example, my mage is Frost/Arcane. My druid is Balance/Restoration. And my warlock is Destruction/Demonology. However, you can only have one build active at a time. So if I'm playing my mage as Frost and want to switch her over to Arcane, I have to stop what I'm doing and activate her other build, which turns off the current one.
Glyphs come in both minor and major and can also help enhance spells and abilities. Most major glyphs will do something useful like boost stats or enhance spells. Minor glyphs are mostly trivial things used for show. Like the ability to change the hair color of a druids shapeshift forms.