For example, suppose you store your visual studio projects in d:\projects. You can create a new "VS Projects" library and include the d:\projects folder in it. This new "VS Projects" library shows up alongside your Documents, Music, and Pictures libraries. From it, you can take advantage of library features shown in the video like the the new views for finding things "by type" or "by date modified" and the search box improvements for building queries.
Your files, of course, remain in d:\projects. The "VS Projects" library just provides you with a convenient way to find and organize those files. If you had a second folder where you keep additional visual studio projects (e.g. d:\moreprojects), you could include it in your "VS Projects" library, too.