Media Views allow you find and use your media files.
They are the modern evolution in Media Center of View Schemes from previous versions. There are a variety of different types of Media Views available, within the Theater View, Standard View, and Media Network systems. For example, in Standard View, there are three top-level Media Views in the Tree by default:
Underneath each of these you will find additional "child" Media Views which can further filter the results, and present them in different manners. Each Media View is essentially a saved search, which allows you to further sub-filter the results using Categories. These saved searches are cascading filters, meaning that the results of a parent View, also limit the results of its children. So, the reason that the views underneath Audio in the tree show only audio files, and not photos and videos, is that the top-level Audio view has a filter that says:
Media Center comes with a stock set of Media Views designed to get basic functionality going as quickly and painlessly as possible. However, this entire system of Views is completely customizable. You can modify the stock views, or create your own. You can even create your own top-level views that combine media types, or show only certain kinds of a particular Media Type.
So, for example, if you want an entire section of the Tree that shows only Classical Music, for example, separated from your more pedestrian "regular stuff", then you can do this!
Media View Types
For further information on Media Views, please refer to the pages for the individual types: