We use the command line to communicate with your computer and the networks it is connected to. Each course goes over every command used, but there's hundreds, thousands more we don't even mention.
If you'd like to learn the basics so you have a more well-rounded understanding of the command line, here are some great resources:
BASH (command line) For Beginners - Kathleen Tuite
Getting to Know the Command Line - David Baumgold
A Command Line Primer for Beginners - LifeHacker
If you find another resource you enjoy, let us know! We'd be happy to link to your recommendation as well.