You can insert a page using +/- menu in the book builder (see below). There are several options for doing this. You can add two pages (a sheet) at the current location. In the example below you see pages 6-7. "Add 2 Pages" will insert two blank pages as pages 6-7. The yellow flower page will become page 8. You can also "Add Left Page" or "Add Right Page." These will insert a blank page as page 6 or 7 respectively, and add a blank page at the end of the book. This is because when you add a page, you're adding a sheet (two pages). You cannot add a single page to a physical book. So we add the second page to the end of the book.