If you are writing an essay on a work of fiction, like one of Shakespeare's plays or a novel like Moby Dick, the introductory paragraph should be a very simple overview about what you intend to talk about in the essay. A good way to look at the organization of an essay is like this:
1) Introduction—you say what you're about to say.
2) Body paragraphs—you say it.
3) Conclusion—you say what you've just said.
This structure makes it clear what the central point of the essay (usually an argument or an analysis) is all about.
If the essay is a more straightforward review, you can introduce the main characters of the story, the main conflict of the story, and the main themes the story touches on. You can compare it to other works by the author or other works of the time period/genre.