The commandline is available on Windows, Mac, and Linux. There are no special requirements, as the command line application ships with the graphical user interface and their installers. If you already installed the GUI, you already have the command line interface. Let's show you where these are.
The commandline interface is generally for advanced users. All functionality between the GUI and Commandline application is identical, with few exceptions. A user wanting to use the commandline application would choose to do so on what's referred to as a headless environment.