When you open iTunes, there are a few aspects to the windows. This is illustrated on the diagram below.
Library - This section includes links to all parts of your library, such as Music, Movies, TV Shows, Podcasts, and Radio.
Store - Previously known as the iTunes Music Store, the Store section provides links to the store and other useful links. The more you interact with the store, the more links will appear as iTunes upates the sidebar on your most frequently used sections of he iTunes store.
Playlists - This section shows playlists you have created in iTunes.Make playlists and they will appear here.
Tracklistings - This section shows the tracks in the album you have selected.