A sandbox view always contains up-to-date copies of all items that have been approved and deployed, whether they are currently available to customers in the store or not. Your sandbox view also contains any changes you have made in that sandbox. Changes that have not been promoted are visible only to the user that made them. Changes that have been promoted but not approved are visible to all users viewing that sandbox, but are not visible outside the sandboxes in which they were made.
When you're on a page where sandboxes are applicable, such as the Products page, a colored bar below the header and above the breadcrumb trail indicates your current sandbox. It also means you can switch to another sandbox.