BTC was created with a new transaction system without a central authority. The BTC can be used in the future as the main currency that we gonna pay with. But what's gonna be the value of a main currency? What's the value of dollars or eur?
-Answer is: The dollar IS the value. The dollar doesn't cost anything. The dollar is the value.
If BTC is gonna be used in future, it not gonna cost anything, because the BTC is gonna be the value. It not gonna be like Bitcoin cost 50,000dollars... Bitcoin not gonna cost anything because Bitcoin IS the value. But that's probably not gonna happen. We not gonna pay with BTC but with stable coins like USDT...
The value of money is expressed through its purchasing power, which in turn is expressed in the number of real goods that you can buy with money. If a loaf of bread costs one dollar, that means the value of one dollar would be one loaf of bread. The dollar itself doesn't have an intrinsic value, it is not used for industrial purposes like gold is, so the only use case of the dollar is as a medium of exchange. Similarly, bitcoin doesn't have any additional use cases besides the medium of exchange, but it is superior to both gold and the dollar because it combines the soundness of gold and the transportability of the dollar. People that appreciate this superiority of bitcoin are willingly accepting it in exchange for services and goods. That is why bitcoin has value.