Think of a significant event that changed you. Possible topics might include

realizing an important aspect of who you are
learning an important skill
gaining a significant insight into other people
overcoming a significant obstacle
realizing something significant about how the world works
Write a personal narrative telling about the event. Describe what happened and demonstrate why it was so significant. Be sure to clearly identify the conflict, build suspense through a series of separate events, describe the climax, and show how it resolves the conflict. Make sure readers have enough details about your experience to picture it in their mind. Use techniques from the descriptive essay to make your story vivid.