Okay kiddo, so a Mac is like a computer that some people use. Normally people use a special key on their Mac called the "Command" key to do things like copy and paste.
But, some people might find it easier just to use one key instead of holding down the "Command" key and then pressing another. This is what we call a "one-key Mac".
It's like having a special friend who knows exactly what you want to do on your Mac and can do it with just one press of a button! It's very helpful if you want to save time or if you have a hard time pressing two keys at the same time.
However, not everyone needs or wants a one-key Mac. It's just an option for people who want a more simplified way of using their computer.