In addition to using the standard methods to control access to pages – ie. by User Profile – you can elect to bypass this and explicitly specify certain Users or User Groups as being able to access the page.
How to make a page viewable only to certain Users or User Groups
Locate the Access Control toggle switch and select “Specify User”
Drag the Selected User or Users into the Invited Users panel
If you have invited any User Groups to the Project you will be able to select them in the Users list and to a specific User Group to the page.