From the US Copyright Office: "Copyright literally means the right to copy but has come to mean that body of exclusive rights granted by law to copyright owners for protection of their work." Copyright exists from the moment of creation and does not require a copyright notice. According to the ALA, fair use is "limited use of copyrighted materials for educational and research purposes without permission from the owners. It is not a blanket exemption. Instead, each proposed use must be analyzed under a four-part test."
Do you have additional questions or concerns about fair use and copyright? Schedule an appointment with a librarian to talk through options for your classes.