I only saw the movie. From what I got from the movie it is about how screwed up the government is the thirst for blood and how they divide the upper, middle, and lower classes of the economy. Kinda like how the Romans did.
People from districts 1-12 are chosen to be in a game, The Hunger Games. Two people from each district are chosen (a girl and boy) from ages 12-18. The tributes are sent to the capitol and they train for the games. When they are in the arena they have to fight to death. The last person who is alive is the winner. But in this case there was two winners. Read the book. It'll explain it better.
A long time ago, the people tried to revolt against the government and failed. Now, the government has these Hunger Games which are supposed to show people how bad life was before the government stepped in, but are really just a way for the government to flaunt its power. The main character, Katniss, becomes part of these games by volunteering to take her sister's place when she is chosen as a tribute. Now Katniss must fight for her life in a battle to the death against highly skilled competitors. And, in a twist, the other tribute from her district, Peeta, has suddenly declared his love for her. The people of the districts, who are watching the games, love this new romantic element, and Katniss begins to use it to her advantage; however, as she and Peeta team up to fight for their lives (the entire time knowing that, if they both make it to the end, one of them must kill the other), the lines between faked and real emotions begin to blur for her, not that she has time to worry about it, because she has now somehow found herself becoming an unwanted symbol of rebellion for the angry masses who are sick of the government's oppression.