On the planet Pandora, there is a valuable mineral that The Company desires. They send in the military and scientists to retrieve it.
However, there are humanoid natives on Pandora called the Na'vi who do not wish their world to be plundered.
The humans create an empty shell that is part human/part na'vi in which certain people can upload their mind to. These are called avatars.
The avatars are used to infiltrate the na'vi population and, after being accepted as one of their own, convince them to relocate.
This world is mind-blowing. The details to the creatures, the scenery, and atmosphere is astounding. You should see this film in 3D to get the full effect. James Cameron is a great creator of worlds. He created the look of the Terminator and the fuller look of the Alien. It stands to reason that, after so many years, he would create the ultimate new world for us to enjoy.
Avatar stars Sam Worthington as Jake Sully whose job is to convince the na'vi to leave. Zoe Saldana is Neytiri - the na'vi who befriends and trains Jake. Sigourney Weaver is scientiest Dr Grace Augustine who does everything she can to be the diplomat to the na'vi.
Rated PG-13 for intense epic battle sequences, you may also want to be mindful that the female na'vi do not wear shirts. They get away with this because they are aliens I suppose.