In the future the america as we know it has collapsed into a dystopian society seperated into 12 districts. Ruled by the wealthy in a place called the capital. The capital, ever year, holds a every man for them self game, the hunger games, in which 2 "tributes' 1 male 1 female (children older than 12 but younger than 18) from each district are chosen at random to compete in the games. In these games only one tribute can win the others all will die by the hands of the other contestants or the landscape in which the games are held (which is in a giant arena)
A girl named katness the main character's little sister gets chosen for the games, she steps up and volunteers to go in her place. The other tribute from her district and her become close, and have to go to the games in which they are put in a position where at best only one of them will survive.
There is a lot more too it but that's a basic run down of the story. the books are great, movie looks like it has some serious potential to be great, or really shitty.