Avatar is a classic of Nickelodeon. It's one of the best series out there. The main character is Aang he is the Avatar. The Avatar is a person who capable of bending all elements and is suppose to bring balance in the world. Aang and friends(Katara,Sokka and Toph) travel through the Avatar world bringing balance around the world. The antagonist is Fire Lord Ozai. Aang ran away from air temple as a child and got caught in a storm. He froze himself for 100 years. Katara and Sokka southern water tribe members finding him. During those 100 years the Fire Nation took over. They have full domination. That's a quick crash course of the lore. You should watch the show after Avatar last airbender there's Korra the next Avatar.