Find the section you want to add your page to in CMS. You should be viewing all the pages in the navigation list where you want to add your new page.
Above the list of pages, click on the Add Subpage button at the top next to the green circle with the + in it.
The Add Page interface appears with three tabs: Properties, Content, and SEO.
On the Properties tab, enter a brief Navigation Title. This is the page title that will appear in the navigation box, so we prefer it to be a single line rather than wrap to multiple lines where possible. Navigation Titles should also use the ampersand (&) instead of the word "and." As you type the CMS will automatically populate the Page Title field with the same title. You can choose to overwrite this field with a longer title if desired. Pages can not be published without this second Page Title field filled in.
If you wish for your new page to be hidden from navigation, uncheck the Visible in Navigation box at the bottom of the Properties tab. You can easily come back later and recheck the box to make the page show up in the site navigation. Hidden pages are available on the live website if you know the URL, but do not show up in the grey navigation boxes on the site. Hidden pages can also be found in search. (See the page about making pages non-searchable for more information.)