Main Idea, Irony, Symbolism
A small, superstitious village holds a lottery every year and the person who gets the slip of paper with the black dot gets stoned to death. They do this because they want the crops to be good. In this lottery, a woman named Tessie Hutchinson gets the paper with the black dot and everyone throws stones at her while she says that the lottery wasn't fair.
The reason the village has the lottery and stones the "winner" is because they want the rest of the village to survive. So really they are wanting their village to thrive but they kill a person every year.
The black box represents fate. More specifically, a blank piece of paper represents another chance to live and a piece of paper with a black dot on it represents death. The black box holds both kinds of papers.