This writing tasks asks you to recount an event from your memory. Do not worry if you cannot remember every last detail, the important thing is that you tell the event in an interesting and engaging way, and you use the past tense to do so.
You also need to use the first person, as it happened to you.
When you put the events into chronological (time) order, it will help to use time connectives, such as later, then, meanwhile, etc.
Remember to vary your sentences and use commas to separate your clauses. Starting with “As I was......, something amazing happened”. is more interesting than “One day I was....”.
Try to spend about 45 minutes on this task.