The larger structure (macro structure) is a cause and effect–because this “event” happened, this was the effect. Within each body paragraph, you should focus on description–providing vivid details to help the reader understand your experience–both physically and emotionally.
The best topic will be a specific event or moment. The more narrow your focus, the easier it will be for you write descriptively. Avoid topics that cover a long span of time. For example, if you were in an abusive relationship, you might choose to write about the moment you decided to leave that relationship, rather than writing about the experience over time.
Think about an event from your past that has made a significant impact on you. Write to explain how the event impacted you using a cause and effect structure. When describing the “event”, be sure to use descriptive details.