First, you need to understand what a narrative essay is. Briefly, a narrative essay is an essay that tells an event from your own experience that is (usually) expressed from a first-person "I" point of view and told chronologically, with events narrated as they occurred in time: first things first and second things second. A narrative essay is built with the same elements that you find in fictional narrative. These elements are: author's tone; character(s); setting (time and place); conflict; plot (as in Freytag's plot pyramid), including climax and resolution: in other words, a beginning, middle and end. The objective of a narrative essay is to share a moment or incident from life during which you gained insight or comprehension. The purpose is also to simultaneously entertain, amuse, inspire, or enlighten your readers.
The first step in forming a narrative essay is to choose an occurrence or incident that had meaningful importance to you because of a lesson (conflict) mastered; importance to your understanding of life, your understanding of someone else, or your understanding of yourself. You might call this an epiphany moment. It might be humorous (enlightenment can come through humor), surprising, mundane, exotic, or a once in a lifetime experience (like witnessing a satellite launch).
Next, you will pinpoint your characters and setting. One character will be you, but what other characters were participants? Were there other participants or did this event happen while you were alone, perhaps on a mountaintop? Then identify the setting: isolate the time and place of the occurrence. Were you five in your parents' rental property? Was it New Year's Eve of 2000 in Times Square?
Perhaps the hardest part is to identify the effect this occurrence had on you. What important thing did you understand better or know as a result of this incident? A correlated question is through what mechanism did the change in you come about: was it what some said; something you thought or witnessed; was it simply the sound of an ocean wave?
With the hardest part done, arrange events in chronological order: "First I, then I, then she, then we," and on until the end. With the chronology in order, identify the climactic moment and the ending resolution (your epiphany). Then identify how it all began, which is the introduction and the inciting action. Now the rising and falling actions (the events before and after the climax) should fall neatly into place.
Finally, remember that to construct your narrative essay, you want to focus on concrete language, not abstract language. You want to tell us that the blue sky was streaked with clouds, not that the sky seemed cloudy; that you pedaled your ten-speed to the dock, not that you rode over there. You also want to emphasize sensory perceptions you had during the incident you are narrating. Say what you touched or felt (I touched the cool rough granite while the wind tickled my arm); what you smelled (cherry pie from the dinner); what you saw (rigid black lava; a field of six-foot high yellow sunflowers); what you heard (a kitten mewing under a concrete step); what you tasted (acrid dust; tart pomegranate).
Using concrete, sensory language will help you develop the tone of your narrative. Is the tone lighthearted; is it somber; is it inquisitive; is it foretelling danger; is it humorous? Following these steps, your narrative essay will practically form itself, with a little dedicated industry and work from you.