It's not much different to digital money. When you log on to your internet banking you see a bunch of numbers, not physical money. Of course with normal currency there's always a physical version.
The "worth" of the currency is simply how much it's valued against more tangible currency at a given time. Kind of like how gold or silver is valued on exchanges. Gold and Silver are tangible items but they are only given value because of humans and how we use them. Same as crypto. If we didn't like the look of silver, for example, and didn't use it widely in jewellery (I know it has other uses too) it wouldn't be worth as much as it is. Bitcoin was born out of the desire to have an unregulated global digital currency - it's kind of become something else now but that's for another day - and grew, initially, because of that.
Crypto only exists in the digital world but that's a huge universe and a growing one. However, unless Crypto becomes more widely used it will eventually die, in my opinion. And I own a fair bit! There are some crypto coins being used by the financial services so if it has a use beyond its basic identity then it might survive, like Cardano or Ethereum.