So what is this film about? what does the title mean? I thought it was going to be a basketball movie or something
I can tell you're not being entirely serious with your question. But at the same time I can't tell if you're at least partially serious. So, just in case you really did want to know ...
the basic premise of the _series_ was :
(nothing here is really a spoiler, it's all revealed in the first episode of the series and is stuff that you can guess)
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Earth, Fire, Water, Air - each element has a nation, and each nation has a set of 'gifted' people that know how to harness their element for attack/defense/support/utility/etc. Every generation has one of these gifted persons (from any one of those elements) who is the avatar (basically, it's the same spirit reincarnated down from lifetime to lifetime). this avatar learns to wield all 4 elements and keeps peace and prosperity between the nations.
However, something happens to Aang (the most recent avatar) and he disappears (in the cartoon series, he is essentially trapped in ice for decades; that is told in the first episode so i'm not spoiling anything). Which turns out to be fortunate for Aang, because the fire nation knows the current avatar is a young boy from the air nation, so they set out to kill all the airbenders. Aang already being frozen, he is spared that fate.
With the lack of balancing force, the fire nation decides to take over the other nations by force.
Aang is freed by a brother-sister pair, and finds out he is in fact the last airbender and the avatar (reincarnated spirit that is destined to be the balancing force). And thus, Aang and his friends that he gains over the course of the series try and hold back the fire nation and eventually attack the nation itself.
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There is a lot more to it, such as the relationships and some power struggles and such. But that's the gist.
Now, what (if any of that) they'll focus on for the movie is anyone's guess