MacOS

You've already got a terminal: Press ⌘+SPACE to open Spotlight, and type terminal to open the terminal. You'll see something that looks something like this:

Where other operating systems use a shell called Bash, MacOS uses zsh by default. For our purposes here, these shells work mostly the same way, but parts of this guide (especially the scripting section) refer to Bash instead of zsh. This is unlikely to ever be important, but it's something to keep in mind.