Full Linux Operating System

You have two sub-options here — a "bare metal" (aka REALLY REAL) or, more likely, a virtual one)

"BARE METAL" Installation Options

Buy or otherwise obtain a Raspberry Pi. (or use one if you already have it)

I put this one first because not only will you learn during this class, you're very likely to find it rewarding beyond this class as well. The Raspberry Pi is a complete Linux computer, usable and used in a VERY wide array of real-life fun and useful projects; ANY model is acceptable, though the later the better; the current "4" is just the small "board," (good for other projects) and there is also the 400 which is embedded in a keyboard. You will likely need not just the board, but a "kit" which includes a case and cords for hooking it up to a TV or Monitor, as well as a mouse and keyboard.

Install on a real computer, dual-boot or or simply wipe the old one.

This is a potentially data destructive process, but I'll be happy to help if you want to try this. Especially good if you have a computer that you're not doing anything with, or you have alternatives to use in case something goes wrong here.

Virtual Installation