visit the loc.gov---copyright section
Here you will find everything you need to copyright any and all of your material. Whether that be plays, poems, song lyrics, music, recording, choreography---YOU NAME IT. The fee is currently $45 dollars per application. I would suggest that if you are submitting material that is by the same author---you should submit everything as a collection. This way you do not have to pay 45 bucks--i.e. per song!