Find out which publishing company owns the copyright to the music you want to purchase. There are several ways to locate this information.
1) Look at the liner notes of a CD.
2) Search the database of a performing rights organization such as ASCAP (ascap.com) or BMI (bmi.com).
3) Search the database of the United States Copyright Office (copyright.gov).
Contact the music publisher that owns the music copyright you want to purchase.
Negotiate a contract with the music publisher to purchase the rights to use the copyrighted music. Let the music publisher know how you intend to use the copyrighted music. For example, if you intend to use the copyrighted music in a commercial, detail the manner in which you plan on using the song. A publisher might not want its music used in certain situations.
Pay the negotiated fee to purchase the rights to use the copyrighted music.
Use the copyrighted music only in the manner in which you agreed to with the music publisher.