The Druid is a hybrid class. They don't really fit into any specific category but they usually take the role of a healer in groups. However, due to their many abilities, druids can also tank, DPS in cat and DPS in caster form. They also have the option of having forms that buff the entire group (such as Moonkin or Treeform). Druids have the capability of taking on the roles of a tank, healer, or damage dealer in an instant.
Shape shifting is something unique to druids. It allows them to take on the shape and aspects of the animals and this is what allows druids to take on different roles. Bear Form, for example, can turn the druid into a high armored tanking bear. Travel form turns them into a cheetah and it makes them run faster. Cat form allows the druid to do more damage and have the ability to stealth. There is even a swim form that allows you to move faster in water.

While the druid is a true, jack-of-all-trades, most druids find it difficult to play all roles equally. Most have a favorite form or a favorite role they prefer to play. They will place talent points into these particular trees to enhance their abilities in those areas. The most common tree for leveling (especially solo) is feral specced. The feral tree allows you to place more points in your animal forms and abilities to help you do more damage.

Druids can make excellent healers, particular when they are specced for Restoration. They have some heals that do greater healer than priest heals and they use less mana. However, they do take longer to cast and can be interrupted if the druid takes damage. Druids also have HoTs (heals over time) which can be stacked with other HoTs and they have the ability Innervate which can be cast on themselves or someone else to regenerate mana while casting. This makes the druid a great supporting healer in a raid setting. They can help support the priest as main healer and provide innervates, HoTs and more.

In addition to being a support healer, the druid can do a considerable amount of damage, particularly when specced for it and do to their versatility, they are very self-sufficient. A druid that learns to make the most of their many forms will rarely have to stop to eat or drink and can continue to take mob after mob. Druids also have crowd-control abilities such as sleeping animals and rooting (used outdoors only).

Some of the challenges druids face is in deciding when to use each form and also how to use each form effectively. Druids have many great benefits such as being able to shapeshift out of polymorph and to be able to heal themselves and get a travel form to allow fast movement speed before the level 40 mount. However, there are some challenges that druids face such as not being able to use certain spells and abilities in other forms and leaning to shift between different bars when shifting forms.

Available races which can be a druid are: Night Elf and Tauren