At school.

I'am at school atm. so I'll write something for ya! Todays topic : Class for me !
Let's get some theory :)

• So you wanna be a warrior , so let's check what WoWWiki said : 

Warriors are melee fighters highly trained in the arts of weaponry. They are strong and quick on the battlefield. As such they can deal large amounts of damage; they are also capable of withstanding large amounts of damage to protect other party members. Warrior abilities depend on rage generation. This is different to all but one melee class, which is the druid; specifically a druid in bear form. Rage is generated through damage being dealt to and by the warrior and is capped at 100. Warriors have several talents capable of aiding rage generation. 

So warrior is a fighter with big sword and big shoulder pads!

• Or holy warrior named Paladin ? What's WoWWiki said ? 

The paladin is a hybrid class with the ability to play a variety of different roles — including healing (holy), tanking (protection), and DPS (retribution). They have auras, blessings and seals that provide useful buffs for other players while withstanding heavy physical damage with plate armor and strong defensive abilities. Paladins are also considered to be holy knights or blood knights.

• Silent killer? Wanna be one of them ? Like previously let's check WoWWiki : 

Rogues are World of Warcraft's premiere melee damage dealer and especially effective in PvP. They have access to a wide range of special abilities, which depend on their constantly refilling pool of energy. Unlike other classes, such as the hunter who has the ability to deal physical damage from a distance, rogues must be in close.

The primary rogue class advantage is their ability to stealth, preventing other players from seeing them unless the rogue is very close and in a 180 degree arc in front of them or much lower level.

 

• Unholy Warrior ? Check WoWWiki : 

Blizzard's original death knight concept was that of an undead spellcaster unit which made its initial appearance in Warcraft II: Tides of Darkness. This death knight could be more accurately described as a horseback-mounted lich rather than the traditional undead warrior. Years later, Blizzard introduced a new death knight hero unit in Warcraft III: Reign of Chaos, and this second rendition was revised to reflect the general characteristics of the more traditional death knight design. To understand the key differences between these two different generations of death knight, see the "Lore" section located further down this page. The death knight was later adapted as a prestige class within the Warcraft RPG and they were former paladin warriors. It is the Warcraft III version of the death knight that became the first hero class in World of Warcraft and was introduced in the World of Warcraft: Wrath of the Lich King expansion. 

• The hunter class performs pulling, threat redirection, crowd control, and primarily ranged damage. Hunters have pets that add to their DPS and help manage aggro. They can also track, tame and train animals and beasts found in the wild. The well trained pet, on countless occasions, has saved a hunter's life. It has been said by many, and throughout history, that hunters consider their weapons and pets to be their only true friends. 

• That was bit of hand to hand fighters lets check evil , dark, haunted caster - Warlock. Let's look at WoWWiki.

Warlocks are former arcanists, or in the case of the orcs, former shamans, who, in pursuit of ever-greater sources of power, have cast off their studies of the arcane or nature magics to delve deeper into the darker, fel-based magic of shadow.

Warlocks are known to slowly damage over time the health of their targets through curses, demonic minions, fear spells, and other magic, including some more direct damage spells

• Don't like Warlock ? Still you can chose a fire/arcane or frost caster - Mage. Hmm... WoWWiki said :

The mage is a DPS caster that specializes in burst damage and area of effect spells. Their primary role in a group is damage dealing and crowd control through the use of Polymorph, temporarily changing humanoids and beasts into harmless critters. At end-game levels, mages' damage is supplemented with spells like Counterspell, Remove Curse, and Spellsteal. Mages' utility spells also include conjuring food and drink and the ability to teleport to major cities and open portals for party members. In PvP, Mage deals ranged damage while using snare effects and Polymorph to control enemy players. As damage casters, primary stats are intellect, spell power, spell hit rating, spell haste and spell crit. Mages do not benefit any direct DPS increase from spirit and this stat should not be focused on, but can however provide extra mana regen which is somewhat handy for mana management.

• Don't like casters damager ? Look at Priest!  HolyWoWWiki :

The priest is the master of healing and preservation, restoring his wounded allies, shielding them in battle and even resurrecting his fallen comrades from death. While he has a variety of protective and enhancement spells to bolster his allies, the priest can also wreak terrible vengeance on his enemies, using the grand powers of the Holy Light to smite and purge them or the devastating powers of the shadow to decimate their minds. The priest is a diverse and powerful class, highly desirable in any group and capable of fulfilling multiple roles.

The priest is perhaps the best healing class in the game with a surprisingly strong damage potential as well (should the player choose to enhance this aspect of the class). Their ability to heal and buff allies, avoid aggro, dispel buffs on enemies, dispel debuffs on their allies, and resurrect fallen comrades makes them an important member of any group, whether it's PvP or PvE. Due to this, priests are one of the most highly sought after classes for any group.

• Or Shamman really universal class. Can be hand to hand fighter , caster and healer. Okey, WoWWiki said : 

The shaman is a hybrid class and depending on how players choose to customize their character's talents, they can specialize in offensive spellcasting, melee damage dealing, or healing. As such, the class is considered one of the most adaptable and versatile in the game. Shamans can also provide support to a group in the form of stationary totems, of which when placed on the ground by the shaman, either provides various benefits to party members, or deal damage to enemies, of which the range is determined by the totem placed.

• Druid like Shamman really universal. Like in paster , WoWWiki.

The Druid is a shapeshifting hybrid class, and is also one of the most versatile classes in the game. As with other hybrids, Druids need to specialize to be most effective in any role. Due to their need to shapeshift to fulfill roles, they can only perform one role at a time; they must switch between the different shapes to adapt to changing situations.