Water, Earth, Fire, Air. Long ago all four nations lived together is harmony but then the fire-nation attached. The avatar was the master of all the elements but when the world needed them the most he vanished.
100 years later my brother and I came across the new Avatar, an air-bender named Aang. His air bending skills are great but he has a lot to learn before he can save anyone.
But I believe Aang can save the world.
I know there has been a little confusion. We are based on the first so they haven't met Toph yet. Aang has only learned air and water.