Song Mode
In song mode the recognizer will recognize both artist and song related things. So you can say key words and phrases like "Gwen Stefani Hollaback Girl" or just "Gwen Stefani". This is a good mode if you want a specific song or you want an otherwise random list of songs by a particular artist.
Album Mode
In album mode the recognizer recognizes key words and phrases from the artist and album columns of the table. Album details are on the right. This is a great way to make sure everything is played in album order.
Artist Mode
In this mode the search recognizer will only recognize artist related things. Details from the current selected artist's works appear on the right. Songs are played in album order.