The Classic layout displays the master data view at the top of the page. The child data views display underneath in their respective tabs.
When a user first accesses a page with a Classic layout, only the master data view will be visible.
If a master record is selected, then a container will appear under the master data view, containing all child data views in their respective tab.
The child data views display detail records connected to the selected master. If another master record is selected, then the corresponding detail records will be retrieved from the server.
You can control visibility of data views on the page with Visible When and Roles properties.