This section covers the use of copyrighted materials in teaching, which could mean content presented in a PowerPoint, readings provided to students in Canvas, material compiled into a course pack or iBook, or any other use of copyrighted materials provided or presented to students in a course.
Educational use of material is always fair use.
A lot of educational use is considered fair, but it is not a given. Teaching is a big point in favor of fair use, but whether your educational use is fair or violates copyright law must consider other factors as well. There is plenty of educational use of materials that does not constitute fair use.
Putting material in a restricted space where only students can access it (e.g. Canvas) is fair use.
Again, this is a point in favor of fair use but it does not necessarily mean your use is fair. For example, you couldn't scan and upload an entire textbook to Canvas and claim fair use because you've restricted access to only students in the course. There are other factors in the checklist to consider.
I can use copyrighted material once, but then I have to get permission.
It is true that repeated long-term use is a point against a fair use determination, but you might not necessarily be violating copyright if you use something more than once. Again, it depends on other factors in the checklist as well.