Page Group Tags, found on the Manage Pages menu, let you assign navigation tags to your website's pages for custom navigation and menus.
You can assign a menu to a Page Group as you would to any collection and have it show only those specific pages.
For example:
If you want a menu to display only pages that make up a portfolio collection of your work, add a tag with a name like 'portfolio' to the relevant pages. You can then add a menu to your website and assign it to the portfolio group and it will only show those pages that were tagged.
To learn how to add Tags to a page click here.
To learn how to assign a menu to a Page Group click here.