iBooks Author: Book pane
The Book pane is an area in the sidebar where you see thumbnail images of your chapters, sections, and pages. From the Book pane, you can add, delete, or rearrange chapters, sections, and pages. You can change between viewing your book as thumbnail images or as an outline.
Change to outline view: Choose Book Outline from the View pop-up menu in the toolbar.
Change to thumbnail view: Choose Page Thumbnails from the View pop-up menu.