An essay is an art that features the elements of the writer's thinking and the writer's voice. Unless you write honestly, with the conviction that comes from using your own voice, you are not writing an essay.
Note: One of the most common errors made by student writers is to write a story or string together a chain of events for an essay. Ordinarily, your voice and ideas, a frame beyond the story itself, must direct any essay, including a narrative essay.
There are different kinds of essays:
The essay most commonly assigned in college writing is the thesis-support essay, which addresses a central question or issue and offers a supporting thesis.
In the humanities or the arts (and sometimes in math and science), you might be asked to write an informal essay, one more exploratory and reflective, developing not 'top down,' by supporting a thesis with reasons and examples, but rather 'bottom up,' by starting with experiences and finding some storyline or trail of explanation.
Many essays blend elements of both the thesis-supported and informal essays. The Empire State College rationale essay, for example, defends a thesis such as, "My degree program answers my personal, professional and educational goals and follows ESC's general and disciplinary guidelines for the academic degree I am seeking." This essay ordinarily details some of your learning autobiography and narrates the story of the research and exploration that contributed to your degree-program design.