Right now, page permissions can only be set at the category level. All pages in a category will inherit its category's permissions.
Categories are set to visible to all your teammates by default. You can also set categories to private, only inviting certain people to view them.
To change the permissions on a category, go to a categories settings by navigating to a category and clicking the 'edit' button in the top right.
In the category settings, you can switch "Who should be able to view this category" to "only certain people".
You can then select the people you want to be able to view that category.
n.b. if you have a community account, all categories will be set to public.