There are 2 ways to jump to different sections within a book:
(1) By making use of Progress Bar: moving the progress bar forward and backward will bring you to different sections within a book. You can access the progress bar by tapping on the center of your device display while reading, the progress bar is at the bottom.
(2) By making use of Table of Contents: at table of Content, tap on a particular chapter will bring you to that chapter of a book. You can access table of contents by tapping on the center of your device’s display, selecting “Go to” icon (the icon with 3 vertical dots and 3 lines), then tapping on “Contents”.