Welcome to "Learn Linux"! Admittedly, the course name is a bit of a misnomer. It's called "Learn Linux" because "Linux" is what most students think of regarding the concepts in this course. A more accurate title might be "Learn to use shells and terminals in a Unix-like environment", but that's a mouthful.
PATH and environment variablesThis course will get you comfortable working on a command line, which is a skill that's going to be critical for the rest of your career as a programmer. So, instead of writing code in the browser, in this course you'll interact with a command line interface (CLI) directly on your machine.
echo "Hello world"
Open the "Terminal" application. You can find it by searching for "Terminal" in Spotlight (the magnifying glass in the top-right corner of your screen).
Open the "Command Prompt" application. You can find it by searching for "Command Prompt" in the Start Menu.
Enable the Linux development environment by going to Settings -> Advanced -> Developers -> Linux development environment. Once installed, open the "Terminal" application from your app launcher.
If you're on Linux, I refuse to believe that you don't already know how.