Q: If there's no specific exception, such as face-to-face teaching, do I have to first ask permission from the copyright owner before I use a particular item?
A: Not necessarily! Remember to consider fair use, which is a more global exception, before determining that you must ask for permission from the copyright owner.
Q: How does licensing play a role in considering whether I can use a particular item?
A: Even if you might otherwise have a specific right to use an item, for instance, a face-to-face teaching exception to show a legal copy of a movie in class, licensing may prevent you from showing a movie from a particular source. Let's take Netflix for example. When you set up an account with Netflix, you agree (in a click through license) to use it only for "personal use." Thus, many experts agree that you generally cannot show a Netflix show in class because you would be violating the license and you can always contract away your rights through licensing.