Sorry for the delay, I’m a check-the-feed-once-a-week type lemming. I love computers, and I admire anyone who also wants to learn; I’m by no means an expert, but I am happy to share what I know.

A distro is a whole OS. An Operating System, as the name implies, is the whole system of software that makes a computer function and interactive (take input from a user, and respond appropriately). This may software definitely includes a Kernel (more on that later), but may also include things like a Display Server (software that acts as an intermediary between gui software and the display/screen), a Desktop Environment (a subsystem of related softwares that handle things like window styles, layouts, and icons), or even utilities (programs that you use to modify the behavior of other programs/processes).

In OSes, there is a fuzzy boundary between programs the user runs, and the low-level processes that run on hardware. This boundary separates “User Space” – programs and processes that run on behalf of the user – from “Kernel Space” – programs and processes that handle the hardware the machine is run on. Where most programs that you interact with are User Space – such as web browsers, video games, multimedia programs, or even most command-line programs – Kernel Space programs are ones that perform tasks like determining how memory is managed, or what processes are running during any given CPU cycle. The Kernel is the set of software that is reponsible for all this “behind the scenes” computer management. This means that the programs don’t have to be written to determine the specifics of the hardware they’re running on, it means that each program you run is much less likely to crash your PC, and it means that it’s a lot harder for malicious software to do serious damage to your PC or OS or other programs.

So that’s the Cliff’s Notes, now the ELI5 analogy version: an Operating System is like a grocery store. The Desktop Environment are all the visual elements that go into the experience, stuff like branding, signs, employee uniforms, displays, even the way the shelves are laid out. The customers are the userspace programs, and that means the employees (and the automated systems that help run the store) are the Kernel. Because the relationship between the customers and employees mostly revolves around the merchandise being sold, the merchandise will be analogous to the computer’s physical resources.

A customer can come in, select what goods they want, and check out, but they can’t stock the shelves themselves, nor order something that isn’t stocked, nor adjust prices, nor open the store if it’s closed. To do any of that, they need to ask an employee to perform those actions, and find a way to deal with it if the employee won’t or can’t. This also means the employees are responsible for opening the store, getting everything ready for the customers, cleaning up after the customers, and locking up the store after everyone’s left. This makes it easy for the customers, because they don’t have to bother with all the work that goes into shipping, pricing, stocking, theft, etc., nor do they have to worry about dealing with every possible type of shampoo they might come across depending on which grocery store they go to.

Also - I have Linux mint - does that tell you what 3 I have and if not how can I find out?

I can figure out 2 of the 3. Linux Mint is the distro / OS, and it runs on the Linux kernel. This is why distros like Arch and Debian and Linux Mint and Nix all get lumped together under the “Linux” label: they all run on the same kernel (and follow the same standards of OS design known as POSIX).

The Desktop Environment (DE) you have depends on which ISO you (or your friend) downloaded from the website, the editions are named by the DE–e.g., if you installed Cinnamon Edition, then Cinnamon is your DE. The other easiest way to tell is to run the terminal command inxi -S – and remember to check the man page for it (man inxi, or online) before running random commands from the internet if you don’t know what they do – and then checking what it says under the section labeled "Desktop: "