All these districts are controlled by the Capitol, where lives the president who is always very, very cruel.
The Capitol, to show the Districts how weak they are and how little control they have, hosts the Hunger Games.
Two tributes are selected from each district to participate in a game. An arena is set up that looks like a natural surrounding {a jungle, rain forest, desert, etc..) Here, the tributes have to try to survive and kill each other off. The one who is the last standing wins and earns food and gifts for their District, and also can never be selected for the Games.
Once chosen, you can't get out of it unless someone else offers to go for you, which no one is entirely willing to do.
To get chosen, your name is written on a piece of paper and put into a small bowl, and is chosen at random. Only children are put once {I believe you're safe at the age of 18}, but poorer families are forced to add their children's name multiple times because the more you put your name in, the more grain you get for your family. Of course, this means you're even more prone to be selected.
Hunger Games is about Katniss Everdeen, a young girl who lives in District 12. Her father died at a young age, and from then on she had to take care of her younger sister Prim and her shocked mother. She snuck out under the electric fence that borders the District, and hunted for food using her bow and arrow.
At the Reaping, which is the time of day where they select the tributes, Katniss's sister is chosen to be in the Games. Knowing that Prim knows nothing of survival, and Katniss is more skilled in hunting, Katniss offers to take her