Think of a story you can tell from your life, an event you witnessed or participated in.
You can write all kinds of things about it without revealing what occurred. The trick is in the details.
As you recall the story, instead of telling “what happened” try to remember the details in the story. (What was in the background? What were people wearing? How was the weather?)
Recount as many details as you can, but don't reveal how they are related to what happened.
Here is a longer version of these instructions.