It's very easy to navigate any story!
Every story has a table of contents. To view the table of contents, all you need to do is click the hamburger button at the top of the story.
After clicking, the table will appear and you can navigate directly to any page in the story by clicking first on its chapter and then the page of your choice.
Or you can navigate a story by progressing the page forwards or backwards by using the controls in the top and bottom right and left corners.