How to get macintosh music?

i want to get the song in the beginning of this video a href="http://www.youtube.com/watch?v=YLP8tXAZKvQ" rel="nofollow"http://www.youtube.com/watch?v=YLP8tXAZK…/a ok in know it is on garage band but how do i get it? theres also alot of other songs i like on mac please tell me how to get it