A Shaman is the spiritual visionary of its tribe or clan. Those healers can see into the world of spirit and communicate with invisible creatures, impossible to see for a normal being.

The Shamans have visions of the future and their goal is to guide their people and protect them during troubled times. Despite a wise and serene behaviour Shamans are dangerous enemies when angered and their wrath is a threat to anyone who dares fighting them.

Originally Shamans were only available for the Horde (Tauren, Orc or Troll) and they were supposed to compensate the absence of Paladin.

With the release of World of Warcraft: Burning Legion, Shamans and Paladins are now available on both sides (Horde and Alliance).

In a group a Shaman is the quintessential fifth member, according to its talents it can either be the main healer (if well equipped) or an assist DPS (magic or melee) and its totems allow him to buff his group.
A Shaman can specialize in elemental magic he will then be a good spell caster with an uber Totem of Wrath increasing the group's critical strike and the chance to hit with spells. He can also enhance his fighting abilities, leading to an effective damage melee damage dealer.
The Restoration tree focuses on the healing abilities of the Shaman; he will then become one of the main healers in a group or raid.