The US Copyright Office provides documentation and information on copyright law, along with forms for registering copyright and other useful information. Sections of interest:
These websites are different in their outlook and may represent the views of commercial entities.
Copyright and Art Issues Copyright Information collected by Christine L. Sundt of the University of Oregon.
There are many videos available at Copyright Clearance Center. https://www.copyright.com/learn/resource-library/
U.S. Copyright Office of the Library of Congress
U.S. Patent and Trademark Office of the Commerce Department
