In simple word. NFT are unique digital assets that cannot be replaced. You can view them but you cannot edit, replace or change them. It started with Ethereum Blockchain but has no shifted to other Blockchains like BSC, Solana and Matic becuase of cheap transaction fees.
So lets say I bought a 7 second clip from the NBA showing Lebron James dunking on two people and made it an NFT. Let's say the same video is on YouTube. First, how do I get/transfer a clip like this or another example like a painting I made on the blockchain? What makes NFTs unique? Is it that I will be the only owner of the clip on the blockchain.