Money is used in World of Warcraft for a variety of purposes. You need it to upgrade your class and profession skills, you can use it to buy consumables, equipment, ingredients and recipes from vendors and at the Auction House (sometimes abbreviated AH in this guide), and it comes in handy when you need to get from place to place on the animal airlines (Flight Paths).
The number one thing that most players want money for is to get a mount at level 30. This guide is dedicated to getting you that first 35 for your riding skill and first mount (factoring in the discount for being honored with your faction). Likewise, characters reaching level 70 will want to acquire their first flying mount as well, which represents another substantial cost.