Music of any genre, any mood, or artist -  Pandora Radio
is a free, easy way to access background music in your classroom.

cattv shows us the basics in this tutorial:

Other online tutorials/info:

https://www.youtube.com/watch?v=Sko_IYdMaxM&feature=related

https://www.youtube.com/watch?v=3B-K1aB_QG0&feature=related