Fair use determines if you can use or reproduce content created by someone else without their permission. Reproduction of materials for teaching may or may not be considered fair use. Generally, to determine if a use is fair it must pass a four parameter test. Otherwise you must seek permission from the copyright holder or use a different work such as one that holds a Creative Commons attribution license or is under the public domain.
These questions are outlined in Section 107 of the U.S. Copyright code.
This LibGuide provides general information that may or may not be applicable in your case. The information included here should not be considered legal advice. Please consult an attorney with any specific questions regarding copyright and fair use.