The phrase end of story is a way to clearly state that there's nothing more to say. If you're tired of explaining why you shaved your head, you might say, "I wanted to be bald — end of story."
End of story is an informal, straightforward way to communicate "I'm done talking." It's often used by people who are convinced their opinion is correct and aren't interested in debating: "My dog is smarter than yours. End of story." It's also a way to signal that you're unwilling to provide further details. If your friends want all the latest gossip about your crush, you might shut it down by saying, "We haven't spoken this week. End of story."