WoW Classes, along with race, are fundamental to what kind of game experience you're going to have in World of Warcraft. There are important differences to consider. Here's a brief overview of each one.

Druid: very versatile class. They can assume different roles, such as tank or mage due to shape-shifting,

Hunter: Only class that uses ranged weapons, also only ones that can name and feed pets.

Mage: Great for direct and area of effect damage. Range magic is quite powerful.

Paladin: Versatile and durable Holy Warriors. Great support class and has powerful buff abilities.

Priest: Can heal whole groups at once. Uses utility spells and mind tricks like Mind Control. Can use shadow magic effectively. They are powerful healers.

Rogue: Good stealth but used primarily as melee due to their incredible physical power.

Shaman: Versatility is great. This class is capable of switching from healer, to caster, to melee DPS. Good for raids because of ability to drop Totems.

Warlock: uses dark magic, curses and demons. This class can summon pets and they are very good for ranged magic attacks.

Warrior: they are powerful class combat fighters, great tanks; they are very dependent on gear to maximize power, can be a bit expensive because of this.

Death Knight (Hero Class): Can raise Undead and has powerful casting abilities. Also a very powerful melee Class.

It is just a very brief introduction of WoW classes and their general abilities. There is plenty of detail to each one, if you don't have enough tine to study up closely, this brief information will help you to gain a basic understanding. This way you can make sure to choose a class that fits you most in the gameplay. Wish you good luck and enjoy it.