There are three basic view settings in the image viewer:
Thumbnails: Allows you to view all of the pages in a work at one time. Double clicking on any of the thumbnails will pull up that page in the sidebar view.
Sidebar view: Allows you to view one page in detail, while providing thumbnail images of the other pages in the work in the sidebar on the left. You can zoom in and rotate the central image using the controls directly above the central image.
Full view: Shows one page at a time in a large window, without thumbnails on the left. You can zoom in and rotate using the controls directly above the image.