The Warcraft universe is vast, storied, and has an incredible amount of lore developed over 30 years. To help make things a bit more approachable, I'll throw together some basic info that'll help you make your character!
Races
Alliance - Proud and noble, courageous and wise, these races work together to preserve order in Azeroth. The Alliance is driven by honor and tradition. Its rulers are champions of justice, hope, knowledge, and faith.
In a time when chaos and uncertainty reign, the Alliance remains steadfast in its determination to bring light to the darkest corners of the world.
Humans: A numerous and spirited race, humans form the backbone of the Alliance, no matter which kingdom they hail from. Ever adaptable, humans are quick to pick up on traits and strategies of their allies and enemies both.
Dwarves: The bold and courageous dwarves are an ancient race descended from the earthen - titan-forged beings of living stone created when the world was young. Although short - scarcely standing over 5 feet, dwarves are nonetheless sturdy and courageous defenders of the Alliance.
Night Elves: Nocturnal, xenophobic, and enigmatic, these elves stand as tall as 8 feet in height, and are characterized by lean, sinewy bodies in dark, cool colors of blue and purple. Savage defenders of their ancient forest homelands, these ferocious elves will fight tooth and nail to ensure their sacred lands are never again tainted by evil.
Gnomes: Clever, industrious, spunky, and not much larger than the children of most other races, gnomes strive to stand out and make their mark on the world, a view often manifested in their wildly styled and colored hair. Their remarkable optimism in the face of calamity symbolizes the truly unshakable spirit of the gnomes, and their boundless creativity and ingenuity is rivaled only by their commitment to the Alliance's cause.
Draenei: Ancient and not of this world, the Draenei - or the Exiled Ones in their own tongue - are refugees from the stars who have made a home among the peoples of Azeroth. Tall and broad, with bluish skin, hooves, tentacles, and odd facial ridges, the Draenei stand out amongst the native races of their adopted world, but nevertheless fight to preserve the light and beauty in all things.
Worgen: Once human, the citizens of the kingdom of Gilneas were afflicted by an ancient curse that turned them into savage beasts. Having managed to wrest back some semblance of civility and control with the aid of the druidic night elves, the worgen stand side by side with the Alliance and unleash their fury upon their foes.
Horde- Driven by unity, the Horde consists of a coalition of disparate races and cultures loosely joined in an alliance of convenience against a hostile world that would see them destroyed.
A faction led by off-worlders and composed of outsiders, the Horde has survived the obstacles of Azeroth by bonding together, fighting as family, comrades, or even uneasy allies. Focused, ferocious, and sometimes monstrous, the Horde values strength and honorand is relentlessly opposed to any who threaten the ideals of freedom and hope.
Orcs: Native to the lush world of Draenor, the massive green-skinned orcs were corrupted by demonic powers and made to invade the world of Azeroth. Eventually able to free themselves from demonic influences, the orcs settled on Kalimdor, erecting their great capital Orgrimmar—from where they fight to find their place in the world they once came to conquer.
Forsaken: Bony, decrepit, and withered, the Forsaken represent a contingent of undead broken free of the Lich King's iron will. Calling themselves Forsaken, they now struggle to thrive in a world that has come to despise their existence.
Tauren: The peaceful tauren - known in their own tongue as the shu'halo - have dwelled in Kalimdor for uncountable generations, striving to preserve the balance of nature at the behest of their goddess, the Earth Mother. Horned, hooved, and often over 10 feet of fur and muscle, the tauren are indomitable warriors, yet are the heart and soul of the Horde, striving for balance and honor in all things.
Trolls: Ancient and mighty, the trolls once had dominion of much of the primordial world. Worn down by conflict, infighting, and outside influences, the once united troll empire has scattered into various tribes, many of which have joined the Horde. Tall and lanky, two-toed and three-fingered, with long tusks and pointed ears, trolls stand shoulder to shoulder with their allies in the Horde, proudly lending their savage might to allies old and new.
Blood Elves: Descended from magic-using exiles of the night elves, the blood elves suffered a decimating attack on their lands by the undead Scourge, losing the vast majority of their population. To honor the fallen, they took the name blood elves - or sin'dorei in their own tongue - and the people of Quel'Thalas worked to rebuild their homeland and help lead their new allies in the Horde into a bold future.
Goblins: The goblins' craftiness and greed make them masters of mercantilism. Reforging old pacts with their one-time allies, the diminutive green-skinned goblins of the Bilgewater Cartel have been welcomed into the Horde. Honing their inherent cunning to a razor's edge, the goblins hope to use their explosive inventions to rule the world – or at the very least own a profitable percentage of it.
Many, many other races exist in the world of Warcraft, affiliated with either faction, both, or none at all! A great many of them make for excellent adventurers, so look into the lore if you so desire, and feel more than welcome to run ideas by me if you want to try something unconventional out!
Classes
Death Knight: Former undead champions of the Lich King, death knights fight with the grim magic of the grave as much as they do with their blades. Wielding dominion over necromancy, blood magic, and frost, death knights are near-unkillable juggernauts, like the slow, inevitable march of death. A mix of magic and martial capability, with dark flair and relentless durability.
Demon Hunter: Fighting fire with fire, demon hunters ritually consume the soul of a defeated demon and cut out their eyes, forever changing themselves to better combat the forces of the Burning Legion. With unnatural speed, agility, chaotic fel magic, and magic-detecting sight, demon hunters are lightly-armored skirmishers that excel in tracking down and dispatching foes.
Druid: Envoys of nature, druids are flexible and adaptive, taking on the forms of all the beasts and birds of the wilds, and wielding potent magics that allow them to revitalize the injured and strike down their foes with the wrath of the heavens. More than mere shapeshifters or spellcasters, druids call on the Wild Gods to imbue their magic and forms with natural might.
Hunter: Cunning, agile, and disciplined, hunters are masters of the wilds, tracking down foes, taming wild beasts to fight by their side, and taking out enemies from a distance or up close. Utilizing traps, bombs, and various other implements, hunters have a tool for almost every situation, and are masters of survival.
Mage: The archetypal caster, mages draw on the power of arcane magic to shape the world around them. Devoted to study and knowledge, mages can assault their foes with raw arcane magic, burn their foes to ash with powerful fire magic, and chill their enemies to the bone with frost magic. Additionally, mages are also able to conjure refreshments, provide transport around Azeroth and beyond with portals, and perform many other feats of magic.
Monk: Masters of unarmed combat, monks internalize spiritual magic to enhance their bodies to superhuman levels, or externalize it in devastating blasts or revitalizing mists. Flexible, mobile, and unpredictable, monks regularly surprise with their unusual fighting styles and uncanny ability to dodge and weave from any trouble that comes their way.
Paladin: Holy and devoted warriors, paladins stand directly in front of their enemies, relying on heavy armor and healing in order to survive incoming attacks. Whether with massive shields or crushing two-handed weapons, Paladins are able to keep claws and swords from their weaker fellows – or they use healing light to ensure that they remain on their feet.
Priest: Religious spellcasters that hail from a variety of backgrounds and faiths, priests balance Light and Shadow magic. Weaving protective magical barriers, smiting the unholy, and mending wounds with one hand, and assaulting the minds of their enemies with the other, manipulating minds and sowing chaos and insanity through the power of the void.
Rogue: Thieves, cutthroats, spies, pirates, and assassins, rogues are masters of cunning, subterfuge, and stealth, utilizing underhanded tactics to achieve their goals. Sneaky and tactical, rogues prefer to ambush their opponents, taking an easy win over a fair fight in almost any scenario.
Shaman: Powerful elementalists, shaman call upon the spirits to aid them in battle, beseeching the elements of earth, water, fire, and air to aid them, as well as powerful ancestral and otherworldly spirits. Competent healers and combatants both, shaman channel their magic through totems - small symbols that dedicate their bond to serving and honoring the spirits that grant them their awesome power.
Warlock: Dark spellcasters that utilize fel, shadow, and demonic minions, warlocks ride a fine line between wielding their dark magics, and being corrupted by it. Harvesting the souls of the slain to fuel their magic, warlocks drain the life from foes, summon and enslave demons, and obliterate their foes with hellish green flame.
Warrior: Heavily-armored and fiercely armed, warriors are a step above the common footsoldier, behemoths that stride the battlefield with soaring leaps, terrify their enemies with howling screams, and cut down their enemies with raging blows. Wielding little to no magic, warriors nevertheless carve a path of blood through battle and the tales of history alike, forged by grit, will, and an indomitable spirit.
The world of Azeroth has many locales, nations, and peoples, but by far the two largest and most important landmasses to this story are the continents of Kalimdor, to the west, and the Eastern Kingdoms, unsurprisingly to the east.
Although no faction can lay claim to the entirety of either landmass, the Horde has the strongest claim to Kalimdor, and the Alliance holds much of the Eastern Kingdoms.
In Kalimdor, the Orcs and Trolls call the red desert of Durotar their home, and the recently nomadic Tauren have settled down in the verdant grasslands of Mulgore at the center of the continent. The night elves control much of their ancient forest lands in the northern half of the continent, and the Draenei occupy the islands of Azuremyst and Bloodmyst Isle far to the north, near the elven tree-city of Teldrassil.
In the Eastern Kingdoms, most humans call the city-state of Stormwind home, near their gnomish and dwarven neighbors in Dun Morogh. The Forsaken hold the former kingdom of Lordaeron and much of its surrounding lands, and the Blood Elves take residence in the northern tip of the continent in the Eversong Woods.
However, threats lurk in every corner of Azeroth, even in the most 'civilized' lands. Monsters, beasts, demons, ancient dragons and horrors without name still control and inhabit vast swathes of the world. Whatever footholds are controlled by the mortal races are tenuous and fleeting, on the precipice of collapse if the wild forces of the world are left unchecked. It falls to adventurers like you to keep your faction, your people safe.