A more thorough explanation:

The Copyright Office is a department of the Library of Congress that manages copyrights in the United States. When someone creates a work that is eligible for copyright protection, they can automatically be legally protected from infringement. However, to bring a legal action for infringement, the person must register the work with the Copyright Office.

For many types of works, individuals also have to send two copies of their work to the Copyright Office or face a fine. The Copyright Office manages the copyright catalog that documents all the major details for every registered copyrighted work, allowing individuals, businesses, and the government to search for existing copyrights.

Besides administering the registration of copyrighted works, the Copyright Office also plays a fundamental role in the policymaking process for copyrights. Congress allocates authority to the Copyright Office for creating regulations for much of U.S. copyright law. Also, the executive, legislative and judicial branches of government look to the Copyright Office for guidance when dealing with copyright issues or changing the current copyright law.

John writes a book and wants to protect his work from being copied without his permission. He can automatically be legally protected from infringement, but to bring a legal action for infringement, he must register the work with the Copyright Office. John also has to send two copies of his book to the Copyright Office or face a fine. The Copyright Office will then document all the major details of John's book in the copyright catalog, allowing others to search for existing copyrights.