You are able to go back to any page within a lesson by doing the following:
Click on Learn from the top navigation menu.
Click on the View Course button to the right of the course icon.
The titles of the chapters/lessons will display. Click on the chapter you want to see.
Once you are in a specific chapter, the drop down Menu button in the upper left of the screen will help you navigate to the desired page. Or, simply navigate through the lesson using the arrows.