As punishment and for remembrance of the war, they hold an annual Hunger Game in which 2 members (1 boy and 1 girl) from all 12 Districts fight until the death to try to win their district food and an opportunity to live a secure life.
The movie has many twist and turns. While watching the movie, I was curious to know about each character and their past. For example, Thresh from District 11 had me wondering how he died and I later found out from a friend who read the book.
So for your sake, since it was never mentioned in the movie, I will give you a little spoiler from the book. In the scene after Thresh had killed Clove who was from District 1, Kato subsequently followed Thresh in secrecy and eventually killed him.
Just little detail like that are very interesting and if you can't get enough of the movie just try to read the book which I will certainly do after school is over!