A copyright protects the creative works that you publish. Every person secures the copyright to their work upon putting it in tangible form, but you also have the option of registering your copyright.
The U.S. Copyright Office explains you do not have to register your copyright to get protection, but registering does offer additional protections.
If you do not register your copyright, you do not have the ability to bring a lawsuit for copyright infringement. It makes it much more difficult for you to protect your work if you cannot take people to court who illegally use it.
If there is ever a dispute over who owns the copyright to work, registering can give you documentation to show your ownership rights. You will get a public record that you can show in court to win your case. This is important even if you are not the one bringing a case to court. Someone bringing a case against you can also lead to issues and could potentially mean you lose your copyright if you do not have it registered.
If you have a registered copyright, you are able to get more damages than you could otherwise if there is a dispute. You can get attorney fees paid for and other statutory damages. It allows you to have more legal standing in making claims and hold people responsible for illegally using your work.
Registering your copyright occurs when you file the proper paperwork with the U.S. Copyright Office. You must go through the formal filing process to secure legal registration. You cannot register your copyright in any other way.