The Warlocks are a great class to play in WoW with a ton of cool abilities and spells at their disposal they truly are a class act. A Warlock will draw their power from mana and will use cool shadow and fire spells and abilities to inflict damage on their opponents.
The Warlocks have one obvious weakness in that they can only armor there-selves with cloth making vulnerable to attacks as well as the need to keep replacing or repairing the armor you're equipped with. However the Warlock is equipped with a number of ranged magic damage dealing spells and has a variety of DoT (damage over time) spells to drain their opponents life continually.
Another nice set of abilities that lends itself to the Warlocks are their fear spells. These can literally stop your foe dead in their tracks and send them running temporarily. Not only is this cool but when combined with the Warlocks DoT spells and ranged magic spells it makes for a good DPS build.
Not to mention that the Warlock class are equipped with a demonic pet that's always by the Warlocks side when summoned and ready to do battle, whether it be the sexy Succubus whipping your foes or the demented Imp minion running like a lunatic blasting your opponents with fireballs.
Warlocks are primarily ranged magic damage dealers although adapt well to different talent builds. A Warlocks main focus though is to take down mobs from a distance with their variety of shadow, fire and fear spells. The talent build you choose for your Warlock will greatly determine the role your character plays in the game especially in group scenarios. The three available talent trees for Warlocks are the Affliction, Demonology and Destruction talent trees.
The Affliction Warlock talent build which happens to be one i'm experimenting with at the moment for one of my alts is focused on the Warlocks DoT spells and Fear spells making it the ideal build for PvP scenarios although not likened by many for leveling purposes.
The Demonology talent build will focus more on the damage output of the Warlock class and that of the Warlocks pet. This talent build is suitable for both PvE and PvP sceanrios and if followed through to the end you'll receive the Metamorphosis ability which will enable you to transform into a demon which is a pretty cool ability.
The Destruction talent build focuses heavily on the Warlocks damage output by acquiring new and improving the Warlocks shadow based spells such as shadow bolt and fire based spells such as Immolate.
When using the Warlock class to create an "alt" character and level through the game quickly the Demonology and Destruction talent trees offer the best specs for a nice Warlock leveling build. The Warlock also adapts well to slight hybrid builds although one should primarily focus on just one of the talent trees to start off with.