Meet Peeta Mellark (played by Josh Hutcherson), who is the son of the town baker in District 12. His name is drawn as the male tribute for the Hunger Games, and he becomes Katniss' biggest ally in the competition.
It's no secret that there's a complicated love triangle between Gale, Peeta and Katniss. But that's about all we can say about that for now. If you want more details, you'll have to see the movie and read the books!
An interesting back story that's hinted at in the movie is the time Peeta once gave a starving Katniss some bread, despite getting a beating from his mother for doing so. We learn he burnt a loaf to give to Katniss, who was in the grips of starvation. The two don't speak again after that earlier incident, and so their being thrown together in The Hunger Games makes for interesting viewing... after all, only one of them can survive.