If you used the Topics layout, each section you have created will be listed on the left menu and on the home page for your course the sections will appear as a list under the course content tab.
If you click on one of the topics, the navigation 'jump to' drop down box will appear which means that you can easily navigate to one of the other topics. In addition, navigational links to the previous and next sections will appear on either side of this dropdown box.
If you have lots of pages in each section, there isn't a similar flow between individual pages or subpages as there is between sections and you will need to set up your own links once you're happy with the order of content.
Setting up the links between pages is described in 'Adding pages' under the heading 'links between pages'. The creators of Observing the Night Sky: What next? used their own image files for the 'back' and 'next' page button links, however text links work equally well.
The book module has arrows to the next and previous pages.