As far as I know, you already owe copyrights to all your songs and everything you create by your own - so you don't have to do something special to obtain these copyrights. If you're concerned with the possibility that someone can say that your text belongs to some other person, you can go some notarial service and try to register printed materials, to get some prior registration day.
I suppose you may find lots of answers here:
http://www.copyright.gov - information of US copyright office.