Page instance
Page instance is where you can find the page-specific, localized content for the modules in the layout, such as all text, images, buttons, marketing-specific content, and more.
The module properties that have not been locked on the page layout, or on the page template level, can be created on the page level.
The page module selection and arrangement are defined by a central, preset layout, which is centrally edited to update many pages. The selection and arrangement can also be defined by an embedded layout, which is private to a single page, though provides the same functionality as the preset layout. An example of the embedded layout would be the home page in the Module library.
The purpose of the page instance is to separate the data entry roles from the design roles. This feature allows a content editor who modifies or creates page instances (for example) to focus on the content instead of the layout and design of those pages.
Watch the following video for a demonstration of how to update and publish a page in the site builder.