NOTE: The Emacs tutorial has lots of weird terms: "Meta key", "frame", "buffer". This is because Emacs started a LONG time ago. Don't worry, you'll get the hang of it with practice.
I have no idea why we make people jump through the hoops of learning archaic terminology, rather than evolving the software to use the terms people actually use today.
The Meta key is called the "Meta key" because that's the label that was on the keyboards of the Lisp machines in the MIT AI lab when Emacs was first developed. It's been thirty-plus years since that key was found on anything close to a significant fraction of keyboards in use in the world. There's no evidence that it's ever going to make a roaring comeback, either.
In other words, the Meta key, as a key, is dead and gone. It is literally as dead as disco! And yet the name persists, even though the way people have interacted with the "Meta key" for decades has been to press a key labeled something other than "Meta."
So: why hang on to a dead word? It serves no practical purpose, and does active harm by confusing people new to the editor.
But no, rather than update our terminology so it bears some resemblance to the world we actually live in, we hang on to it and tell newcomers that to learn Emacs they're just going to have to get used to pretending they're working on a space-cadet keyboard, because that's The Way It Has Always Been Done. Sigh.