Don't buy the guides. Not the World of Warcraft one or the World of Warcraft: The Burning Crusade one. It's an MMORPG. Ask people in the game. Or ask here. The information in those guides tend to get outdated since the game evolves. Check out wowwiki.com for a lot of info.
It seems like you're curious about tradeskills. Here is the low-down on them.
There are two kinds of tradeskills, primary and secondary. You can learn all of the secondary tradeskills but only two of the primary ones. At any time you can unlearn a primary one to learn a new primary one.
Secondary tradeskills currently include First Aid, Fishing, and Cooking. Almost everybody uses First Aid at some point, many use cooking once you get it higher in level, and not that many people currently Fish due to the fact that it's boring.
All the other tradeskills are primary ones. Mining, skinning, and herbalism are considered "gathering professions" by the general populus simply because they are the tradeskills with which you "gather" items from the world. These tend to be the more profitable ones overall because they are raw resources. The other tradeskills are leatherworking, blacksmithing, alchemy, enchanting, tailoring, and jewelcrafting. Typical combinations that people pick are the following although you are free to pick whatever combination you desire.
Leatherworking & Skinning
Blacksmithing & Mining
Alchemy & Herbalism
Enchanting & Tailoring
Jewelcrafting & Mining
For all but the Enchanting & Tailoring combo, the gathering primary skill is used to facilitate the leveling of the crafting primary skill. Enchanting and tailoring are commonly used together as people will disenchant their tailored items to enchant other things. You are free to pick any combinations you want though. If you want to do skinning and jewelcrafting or tailoring and leatherworking you are free to do so.
If you want to find out where the trainers are for the various professions your best bet is to ask a guard. They'll tell you where a lot of things are located actually.
Enjoy the game!