During character creation, you will choose a race. Not only does race give different bonuses to different stats, but they also determine which of the six origin stories you play through at the start of the game.
Here are brief descriptions of the three races.
Human
The most numerous, yet the most divided of all the races. Only four times have they ever united under a single cause, the last being centuries ago.
Religion and the Chantry play a large part in human society. It distinguishes them culturally from elves and dwarves more than anything else. Humans can be warriors, rogues, or mages.
Elf
Once enslaved by humans, most elves have all but lost their culture, scrounging an impoverished living in the slums of human cities.
Only the nomadic Dalish tribes still cling to their traditions, living by the bow and the rule of their old gods as they roam the ancient forests, welcome nowhere else. Elves can be warriors, rogues, or mages.
Dwarf
Rigidly bound by caste and tradition, the dwarves have been waging a losing war for generations, trying to protect the last stronghold of their once-vast underground empire from the darkspawn.
Dwarves are very tough and have a high resistance to all forms of magic, thus preventing them from becoming mages.