This displays your story with black text on a chrome background, and as a player clicks links in your story, the text expands. A player can review earlier passages of your story by scrolling upwards. This approach is called stretchtext. They can rewind to past passages to try different choices by simply clicking the links in those passages (but you can optionally disable this in StorySettings).
The StoryMenu in Jonah is simply the box in the upper-right corner.