A narrative essay tells a story - biographical and autobiographical novels could be described as narrative because they give personal accounts. As a device for telling a story, presenting the events to be included in the story in some sort of time-related order helps the reader to understand the action. However, use of techniques like flashbacks or flash-forwards can add to the interest and effect of your essay.
A narrative essay needs to start with its plot. The author needs to determine the conflict, the rising action, the climax, and the falling action and establish the characters to be involved in the story. Use of literary techniques at certain places or to add certain kinds of impact, tension, or surprise needs to be planned, depending upon the way in which the plot is presented and how the action develops.
The method of starting a narrative essay depends upon the author and the plan for the essay. If the essay is going to be completely chronological, the first sentence may start to introduce the main character and the conflict facing that character. If the essay is going to use flashbacks, the opening point may be the main character remembering something that has already happened.
Once begun, the narrative proceeds to reveal the plot, using whatever techniques the author wishes to incorporate into the storytelling.