To add or edit a page, you can either use the buttons on the top of the page structure (1) or use the context menu (2) that appears when you right-click on a particular page.
If you use the "Add Page" on the top of the page structure (1) a page will be added to a sub-page of the selected page. Click edit button to edit the selected page.
If you right-click a context menu appears (2). There you can add a new page or edit the page you are on.
Want to add to a page on the root level, right click on root ("manual.desti.no" in this example) and select "New Page". The new page will then be added to the bottom of the list and at the root level.