If you had no idea what the literary elements are - you are probably wondering which ones would be the easiest to write about. I would suggest, like Missy, you identify three. In fact, her prompt is perfect and will get you started on the right track immediately. If you are only going to go for three, they need to be three biggies.
1. CONFLICT: no such thing as a story without a conflict. Write about the main conflict that the story centers around, internal or external.
2. SYMBOLISM: is there any person or object in the story that obviously is meant to be symbolic of a deeper meaning? (My guess is probably.) Go with it.
3. THEME: every major work of literature has more than one. This should be easy. (Read the thread posted below.) This makes a great ending too because essentially it allows you to wrap up with the meaning of the story.
Then you can spice up the rest of the paper by referring to the main character as the protagonist and his enemy as the antagonist. Some others found in every great book include the climax and resolution (plot elements). If you want to talk about a major character and any great changes he/she goes through, this is the element of characterization.
Literary elements are words like suspense, plot, mood, metaphor, simile, personification and characterization.
I would assume your English teacher is expecting you to write an essay about something you have recently read. If that is the case, a good thing to do would be to find 3 literary elements that are at work in that piece. Those could be your three body paragraph topics.
Then, write a thesis statement in your intro that matches this pattern: Author's name's Great Book That They Wrote demonstrates the literary elements of __________, ___________ and _________ creating a timeless piece of literature for all generations to enjoy.
Your prompt may require something different, but that should give you an idea and then some.