Copyright (Title 17 of the United States Code) is an intellectual property law that protects authors/creators' works and gives the author exclusive rights to it for a period of time. These works must be in tangible form and can either be published or unpublished. You do not have to register works with the US Copyright Office unless you file a lawsuit for infringement of your work. Check the resources to use tools to help determine the status or length of copyright of a specific work.
What is Fair Use?
Fair Use deals with exceptions and limits to US copyright law and may allow you to use copyrighted material without having permission from the creator. Uses falling under this category include criticism, comment, news reporting, teaching, scholarship, research, and archiving purposes.