Well, the story goes like this: It takes place in the future country of Panem (formerly North America) and there are 12 Districts. Originally, there were 13 but District 13 got crushed in a rebellion. Anyway, each district must send two "tributes", one boy and one girl, to fight to the death in the Hunger Games. The purpose is for entertainment to the Capitol (the bad guys) who are the higher class of people. So yeah, it's like a really intense game show.
Because the capitol wants to onyesha the other 12 districts that it controls them, so every mwaka two children between the ages 12 to 18 (a man and a woman per district) is drawn to be in this arena (the hunger games) and they fight to the death in till one is left standing and they are the winner of those games.