Record the song you wrote and save it as an MP3 on your computer's hard drive.
Go to the United States Copyright Office's official website at www.copyright.gov.
Click on the "Electronic Copyright Office" icon and continue until you reach the Electronic Copyright Office system.
Create a new account at the Electronic Copyright Office, if you don't have an account already, and log in to start the application process.
File a "Performing Arts" claim and fill out as much information as you can concerning your copyright, such as the year you finished writing the song, your address and the author of the song--yourself in this case.
Pay the registration fee by entering your credit card data. The fee is $35 as of 2010.
Upload the MP3 of the song you wrote to the Electronic Copyright Office system.