Okay, let's say I gave you a number.

I hold in my possession an equation which produces another number should you give me yours to process.

One is a lock, the other is a key. This is cryptography terms, thus the "crypto" name for the currency. To reverse engineer the solving of the equation takes time. That's why bitcoin farms and the like exist, because they have to process the equation backwards to receive their certificate. As more certificates are granted, the longer each certificate takes to make, so there's a point where a bitcoin will take longer than the human lifespan to authenticate, at which point, unlike our Federal Reserve, you can't just print more of the things.

This makes it good for a currency form.

There are many potential equations which process that number into the other. If we choose just one of those equations, however, then there is only one input number which produces the outcome outcome number.

If I, the rights holder to the equation, offer to certify your number, then it has a "tangible" worth because there is only one of those certificates in the world.

This is how normal crypto currency works. You are trading certificates which represent a working mathematical equation decryptions. You're allowed to do this, legally, because it counts as intellectual property. It also goes through an internet blockchain, but that's just for authenticity purposes -- to ensure you're the only holder of the certificate.

NFTs supposedly take it to the next level. Images are effectively a string of numbers and symbols which can also be used in the crypto equation. So, then, why not use those 0s and 1s and certificate an image?

And so, the blockchain backend, which represents your "ownership" of the encryption can be viewed in its original form, as a digital image.

You can trade these, just like cryptocurrency, but they just also happen to have a visual representation. If you change a single pixel, however, it also changes the 0s and 1s and you don't have the same ownership of the crypto certificate. That means, there exists a single, legitimate image for that NFT.

Which means they can be traded like cards, except unlike cards there is potentially only one of each.

This is generally how it works, and I left out a ton for the sake of "simplicity", but it's safe to just treat NFTs like a magician's deck of cards. "Pick a card, any card" and that's your card. It goes through some magic, but you have some degree of assurances by the owner of the deck there is only one of that card you picked.

If you don't trust NFT's that's fine, because you aren't obligated to trust a magician either. I don't invest in them because of that. It's fun and exciting, but ultimately all crypto, just like anything else, is only worth something if you find someone who wants it.