Things are related when there's some connection or similarity between them. The fact that you caught a cold might be related to the fact that the kids you babysat sneezed and coughed all night long.
People are related when they share a family connection, and other things are related by different kinds of connections. One poem is related to another if they come from the same school or movement of poetry, and a boy's dislike of baseball is probably related to the fact that his first coach yelled a lot. The verb relate is at the root of related, from the Latin relatus, "brought back."