Include another existing page into current one 

In the white textbox enter the Meta ID of the page that is to be included in the present page. Then click on Save button. The included page will be shown where the special box was located.

If a page already is included in the current page, then a special box will show the Meta id of the included page and Edit page link, which opens the included page in new window where you can edit it.
NB! The included page cannot be edited with current page at the same time.