If you haven't read the book yet, which would just be sad, you absolutely have to pick it up. It's amazing. Plus, again, distance between reading the book and watching the movie is always good. Here's a quick summary. Hopefully the movie follows it's source material pretty faithfully.
Jonas's world is perfect. Everything is under control. There is no war or fear or pain. There are no choices. Every person is assigned a role in the Community. When Jonas turns twelve, he is singled out to receive special training from The Giver. The Giver alone holds the memories of the true pain and pleasure of life. Now, it is time for Jonas to receive the truth. There is no turning back. Quoted from Goodreads