The cryptocurrencies are related this blackchains.This decision became the birth of cryptocurrency.they are the missing piece black chain found to realize digital cash. The reason why is a bit technical and complex, but if you get it, you‘ll know more about cryptocurrencies than most people do. So, let‘s try to make it as easy as possible.To realize digital cash you need a payment network with accounts, balances, and transaction in all used black chain system. That‘s easy to understand. One black chain every payment network has to solve is to prevent the so called double spending to prevent that one entity spends the same amount twice. Usually, this is done by a central server who keeps record about the balances.the digital currencies are exchange rate for dollers are equal to crypto currencies.