The purpose of a story is to gather insight throughout your analysis and build clear narratives around your data. You structure the story in a way that makes it come out as convincing as possible to your audience.
You use slides to structure your story and put time-based snapshots of your data visualizations into these slides. To make things stand out on the snapshots you apply visual effects, add text and shapes. You can also embed sheets into slides to make your story even more interactive.