Quick explanation for those unaccustomed to these kind of viewers.
First, each square on the top will link you to a point in the chapter. For example in chapter 1, there are 49 pages and it doesn’t make sense to have 49 squares. So one will get you to page 1, the next to 7, the one after that to 14, and so on until 49. To move from page to page in order use the arrows.