Sometimes it’s useful to be able to combine multiple pages into a single navigation item. You can do that with drop down menus, or by creating an “index” page, which is what this article covers.
From the “Pages” section of your control panel, click “Create a new page”.
Choose "Thumbnail Grid" from the menu that appears.
Now you can drag/drop pages into the page you just created, to add it to the group.
To choose which image serves as its page's thumbnail, click the small star icon at the bottom left of the image's thumbnail.