It’s assumed that you have a good working knowledge of firewalls from the pre-requisite classes. But if you feel like you’re knowledge is lacking, or you need a refresher here are some tutorials that may help. You can always do you own research, and if these no longer work just fire up your favorite search engine …
What is a Firewall and How Does It Work? From Digital Ocean
Firewall Basics (Video)
What is a Firewall? (Video)