Wwwwwelp, let me take a shot at it. *cracks knuckles*
Okay, so: you know how there are people who collect currency (the traditional, paper-and-coins type)?
And for some people, the specific thing they collect is “bills with unusual serial numbers”:
https://rarest.org/stuff/dollar-bills
So if you find a $1 bill with a serial number like “010101010″, a collector might be willing to pay $50 for that bill.
In general, currency is “fungible”, which just means interchangeable. If I loan you a $1 bill today, and you pay me back tomorrow with a different $1 bill, same difference, that’s an equal exchange.
But if you find a person who specifically thinks Bills With Weird Serial Numbers are a neat thing they like having -- they’ll pay extra for the weird $1 bill. And they wouldn’t be willing to swap it for some other $1 bill with just any non-remarkable serial number. It is a Non-Fungible Bill.
...to the collector, anyway. Not to anybody else! You can’t take it to the grocery store and say “please give me $50 worth of groceries for this $1 bill because the serial number is interesting.”
(Although, hey...if you had a way to convince lots of people that (a) all of them should turn into collectors and (b) every single random serial number is a special one they should pay extra for...that sure would be a way to make a lot of money, huh?)
Non-Fungible Tokens are the same idea, but with cryptocurrency.
Bitcoins have ID numbers. (Same with any other crypto token -- I’ll just use Bitcoin as our example here.) If you can find a collector who likes Bitcoins with weird ID numbers, maybe they’ll pay you 50 Bitcoin for it?
...okay, it turned out nobody cares about Bitcoin ID numbers for their own sake.
But! The ID can be used in a URL.
This is where the art comes in.
You upload an image to that URL. Then you tell people “look, if you buy this token from me, it’s like you’re buying the image! Art collections are fun and interesting, right? Someone give me 50 Bitcoins now.”
Note that the file doesn’t need to be personalized, or unique, or anything like that:
You can upload literally any file at that URL
You can upload someone else’s art
You could upload the same file to 20 different URLs, and sell 20 different NFTs of the same art
You could load the page for a token someone else owns, download the file, and directly re-upload it to the page for a token you own
The whole server could go down, and the URL from your token could be a 404 error for the rest of forever
So if you’re thinking “this sounds like a stupid deal that makes no sense” -- you’re right! You are understanding the situation perfectly. This is total stupid nonsense. For the buyer.
For the person who owns some Bitcoins, and would like an easy way to turn them into even more Bitcoins? This is a fantastic racket.
Pay me a ton of tokens -- or, preferably, the US$ equivalent of tons of tokens -- for this single token I have! It’s totally actually worth that much, I promise.
Also, go ahead and Venmo me $50 for every random $1 bill in my wallet. This is a great deal for you.
And if you believe all that...I’ve got a bridge to sell you.
Sidenote: the “environmentally unfriendly” part isn’t about material, it’s about energy. Producing and exchanging cryptocurrency takes an obscene amount of computing power, which uses an obscene amount of electricity. And it’s not a special thing about NFTs -- it’s how all cryptocurrency works.
(A comparison I saw recently is, at the current rate, “people mining Bitcoin” for 1 day uses about the same amount of energy as "powering every commercial building in the United States” for 2 months.)
Sidenote 2: pretty sure the reason so much NFT art is ugly is, most of the Actual Artists have thought about it for 5 seconds and realized it’s a big racket. (Or been warned off it by other Actual Artists.) And the people who want to buy Actual Art are commissioning the artists directly, same as always.
So the people left in the NFT-buying scene are mostly people who...don’t care about the art quality at all. They just want in on the hype.