Pages
A layout is a vertical stack of spreads — a single page each, or two facing pages once facing pages are on (the first page then stands alone, to the right of the spine).
Adding and reordering
Use the pages sidebar to add spreads and drag them into a new order; the stack reflows and every image keeps its place on its spread. Deleting a spread removes the images on it (you're asked first). Add, move and delete can all be undone.
Navigating
Click a spread in the sidebar to jump to it; the sidebar highlights the spread under the centre of your view as you scroll. Preview mode clips everything to the pages and hides the guides — what you see is what prints.