Copyrighting a piece of writing protects your rights to use that material exclusively, and to charge others for the use of that material, as well as seek damages if it is used without your permission. You can file an application for a copyright on a piece of writing electronically, at the website of the U.S. Copyright Office.
Create a read-only electronic copy of your original work. The writing can be submitted in a number of file formats. Check the Copyright Office's website for more information.
Go to the Copyright Office's website (copyright.gov), and fill out the application form. Upload your read-only file and pay the fee, which was $35 as of September 2011.
You will receive a copyright certificate in the mail if your application is approved. Meanwhile, if you are concerned about presenting and protecting your work, you may mark it as "copyright pending."