Write an essay in which you tell me about your three favorite stories of all time. This is to be a five-paragraph essay, including an introductory paragraph, three body paragraphs (one paragraph for each story), and a conclusion paragraph. In each body paragraph, tell me about the stories themselves, the way you feel about them, and how you encountered them. Notice if all of the stories have anything in common with one another. This paper should be 750–1,000 words long. Try to make your reader really see what you love about each particular story.

This looks like a general literature/writing assignment, intended in large part to display your mastery of writing's technical side. Therefore, when you submit your essay, be certain you have taken all effort to provide correct grammar and syntax, and be sure you've adhered to the five-paragraph format.
With that being said, if I were to give any advice for answering an assignment like this one, it would be this: when it comes to choosing any three stories, be sure to think deeply about just what it is that makes these stories worth reading in your experience. Are there certain genres that you find interesting, or certain themes, or even certain preferences in terms of literary conflict? Do you have a preference for certain character archetypes, or certain genres, or certain character archetypes within certain genres? You can also discuss the plotting of a story, or the writing style of the author who wrote it. These are just a few of the questions that you could ask of the texts (there are a lot more). In any case, when it comes to selecting three stories, I think it would be valuable to think about these sorts of questions and try to identify just what it is that makes these stories so effective. In doing so, you may be able to draw points of comparison and points of contrast, which are always very valuable in an assignment like the one you've been given.