What are NFT? How is that artist are earning more than 50 million in blockchain markets?

NFT stands for "non-fungible token." This kind of token is like Bitcoin, except while you can trade Bitcoin and have more of the same thing that represents real money at a varying market value, each NFT is unique. You possess the token that says you own something, like an art piece, and you can trade it, but if you do, you'll be getting an entirely different piece. To keep all the parts in place, there's enforced (artificial, but isn't everything?) scarcity.

It's easy enough to wrap your head around the fact that a piece of art can be created and exist on a screen, be it your phone, computer, tablet, etc. Then, that piece of art can be seen, screen-shotted, and downloaded by anyone online. But the deeper concept of NFT art is agreed-upon value and ownership; even if anyone can see, download, print out and hang up a piece of digital art, only a select few can actually own that exact piece. So NFTs are a form of digital asset, whose ownership is recorded on a blockchain. What's a blockchain? Good question. Picture a ledger that lives online, keeping a publicly accessible record of who owns what, similar to the kinds of networks that ground cryptocurrencies like Bitcoin or Dogecoin. NFTs are connected to the Ethereum blockchain like this: you buy a NFT (say a piece of art from Beeple Crap) and the unique bit of information about that artwork—including its smart contract—is stored on the blockchain. It proves you own it.

https://www.esquire.com/entertainment/a35742083/what-are-nfts-explained/