Storybook for React Native is configured out-of-the-box in DEV builds only (local device or simulator). You can access it in the Side Menu by clicking on "Storybook".
Sample "stories" are available for the generated components. They allow you to preview the components in various states, dependant on the props passed to them.
Use fixtures (JSON files containing sample data) to write stories for your own components.
For more information on Storybook configuration and writing stories, check the official Storybook documentation.