No matter how well and carefully you've organized your work if you can't navigate that organizational structure easily, there is little point in having it. It event could be argued it does more harm than good. For larger books with a more complex structure this becomes quite relevant, and not getting lost within it means a great deal.
That's why you get a multifaceted and granular look at your book's structure. The main navigational control is the explorer, the tree-like structure in your left sidebar. Every time you select a binding section (e.g., a Manuscript or Binder), you will note that there are three ways of looking at its contents:
From within any mode of browsing the binder's content, you can readily open a particular section and resume working on it.
The List mode, well, lists all the contents of the selected binder, of all types, and on all levels. The list can be filtered to narrow it down, to more easily find what you're after.
The Text mode lists only the Text sections inside the binder, from all nested levels, in a continuous body of rich text that can be edited in place.
The Preview mode outlines all the publishable content inside the binder, on all nested levels, as it would look when published.
Searching within a book
Yet another means of finding content is by directly searching for what you need.
Let's see how all of the above is accomplished, using this very user guide as an example.