We use a mouse or finger to click icons and access files, programs, and folders on our devices. But this is just one way for us to communicate with computers. The command line and the shell make up a quick, powerful, text-based interface developers use to more effectively and efficiently communicate with computers to accomplish a wider set of tasks.
If interested in learning the basics, we'd recommend the Learn the Command Line course. To view all of the courses that cover Bash/Shell, please see our Bash/Shell course catalog!