"Views" are used to "sub-divide" the library into manageable chunks. They do not actually divide the library. They allow you to view just part of the library at a time. The default ones are Audio, Images and Video and, under Audio, Albums, Artists and Genres, but you can create as many vies as you want. Many people with large libraries use Panes to view their library. It is more of a computer view than Categories, which is a more visual way to view the library. Just depends on what you are comfortable with. To change between Panes on Categories, right click on the View and choose Customize View. Then select Panes or Categories.
To create a new view, right click on Audio (or other entries in the "Tree" on the left) and select Add Library View. Then modify the View using Set Rules for Display to show just part of your library, like Classical, Jazz, Blues, Folk, Rock, Pop etc. it takes a bit to do the first time, but once you have done it you can create any views you want.