Copyright law is tangled and messy and it can be difficult to navigate. If you have any questions at all or just want to run a specific scenario by me, please don't hesitate to get in touch. During the COVID-19 pandemic, I am working off campus and only half time. Email is the best way to get in touch. It may take me a moment to respond to your email due to my limited hours of availability, but I will try my best to do so promptly. I'm happy to have virtual conversations over Microsoft Teams, Google Hangouts, or Skype if you'd prefer to meet face-to-face for a consultation.
Stanford's resources, written by a lawyer, offer basic definitions as well as historical context. They also keep a running list of examples of precedent-setting fair use cases and how they were decided.
For those looking for more in-depth resources, especially those designed for librarians and information professionals, ACRL's Scholarly Communication Toolkit has a helpful list of publications and courses.
Copyright.gov is an authoritative and regularly-updated resource. It includes some information on the impact of COVID-19 on Fair Use. The actual laws are posted on the https://www.copyright.gov/title17/ page, broken down into sections.