You are the Avatar, the human embodiment of light and peace and master of the elements. Not only can you bend the four standard elements of fire, air, water and earth, but you can also bend life energy itself: With training, you can use this to give and take away bending to others. You also learn how to bend at an accelerated rate, about three times as quickly as an ordinary bender.
As the embodiment of the Avatar Spirit, when you die, you will reincarnate without memories for the rest of eternity, though you can recall memories from your past lives and commune with them with training. You also retain any other powers you have throughout your reincarnations.
Due to being part-spirit and possessing an innate connection to the Spirit World, you can communicate with spirits, as well as cross over into the Spirit World through meditation. Your greatest ability is the Avatar State, allowing you to harness the combined knowledge of all your previous incarnations, greatly increasing your capabilities (and temporarily negating any memory-removing drawbacks, if you have them). However, this does have one weakness: while in this state, the Avatar Spirit can be harmed. If you were to be killed while in the Avatar State, the cycle would break and the Avatar would cease to be.