Kurt,
The film is about a young teenager who has a school project to think of something that would "make a difference" in the world. So he thinks of the idea of doing a few really major good deeds for people he doesn't even know, but telling them that in order to repay him they should "pay it forward", that is, do a few really major good deeds themselves. He is mocked in class, but what no one knows is that the idea is already catching on.
Much love,
Larry