Every page has options to give it a unique configuration. You can handle that configuration at the individual page level or configure a Page Set of public or private pages all at once.
When you configure options across Sites, Page Sets, and individual pages, there is a hierarchy that flows down. For example, you can set a theme at the Site level that applies to all pages within a Site. You could then set a different theme for the Private Pages set. You can even set a different theme for a specific page that is different than the master site configuration or the configuration for its page set.
When configuring pages, be aware of your context, so you don’t configure an option that you intended for the whole site just on one page—or change the whole site’s configuration, when you meant to change it for only a specific page.