In order to have your students do an audio story, you need to approach it as you would any story or poem or essay. Here is an idea for a podcasting assignment that helps you and your students understand how to do it.
1. Brainstorm. Have your students think of an emotional moment in their lives; it could be an event, something that happened to them or something they witnessed; it could be something that they remember clearly about something they're passionate about -- a great play on a soccer field, or stepping onto the stage in a play. What happened? What was the drama? Why was it so memorable? What details do they remember? How do they tell the story? How do they start?