Jamie Foxx breaks it down for Entertainment Weekly:
After being sent to a chain gang after rebelling against his owners, Django (Foxx) is recruited by a German bounty hunter (Inglorious Basterd’s Oscar winner Christoph Waltz) to help him settle an old score. Django has information that Waltz’s Dr. King Schultz needs, so the German mercenary liberates the slave and promises that if he helps him kill the Brittle brothers, Django’s old owners, he’ll make it worth his while. “He says, ‘I’ll kill ‘em, and you’ll get some money and be on your way as a free man,’” Foxx says.
Along the way, the duo end up crossing paths with Leonardo DiCaprio’s hammer-wielding character (below), a deranged plantation owner named Calvin Candie, who likes to make his toughest slaves fight to the death in gladiatorial combat. “Candie is a businessman who owns a plantation called Candie Land, and that’s where my wife ends up being,” Foxx says. To find her, “we have to get in good with Candie, by me playing a valet for Christoph’s character.”