Copyrights, trademarks, and patents are used to protect intellectual property. The difference between them is what they protect. Copyrights are most often used to protect creative works such as writing, music, or photographs. Trademarks protect a company's product or services; however, it is not formally "on the books" unless it is a registered trademark filed with the US Patent and Trademark Office. Patents protect innovations.
To register a copyright, you must file with the United States Copyright Office. It is advised to pre-register if you feel your works may be infringed before you release them. If you feel your creative work may have value, you may benefit from protecting it before you finish the project.