In addition to automatically making playlists of songs that will sound good together from the music you already have in your iTunes library, iTunes Genius can help you discover new music at the iTunes Store based on the music you already have and like.
It does this using the collective intelligence gathered by all the iTunes users running Genius, purchases at the iTunes Store, and other factors.
In order to have Genius suggest new music to you, just need to follow these simple steps.
Begin by ensuring that you're running iTunes 8 or higher and have Genius turned on (which means having an iTunes account and being signed into it). While iTunes 8 is the minimum to use Genius, the instructions and images in this article use iTunes 11 and higher.
Next, click on the Album view across the top of your music library. This will show your iTunes library as a series of album covers, alphabetized based on the name of the album.
Navigate through your iTunes library to the album you want Genius to use as the basis for your discovery of new music. This will open reveal all the songs on the album.
At the right side of the section that just opened, you should see two options: Songs and In the Store. Click in In the Store. This contacts the iTunes Store and downloads the Genius recommendations for this album.