Copyright is protection provided by law (17, U.S. Code §102) to the authors/creators of "original works of authorship," expressed in any tangible medium of expression.
This protection is available for original works from the moment they are created in a tangible medium, and it applies whether they are published, unpublished, or registered with the U.S. Copyright Office.
However, there are exceptions to copyright that allow works to be used for educational purposes. Such exceptions are benefits for all.