Cryptocurrencies are valued on a number of different factors, the most significant of which, is supply and demand. The scarce nature of cryptocurrency plays a part in the value of the various coins, as most of the more popular coins have a finite supply. One example is Bitcoin, which has a finite supply of roughly 21 million coins.
However, the price of cryptocurrency is also affected by the energy consumption required to mine it, blockchain difficulty, how easy the currency is to use, public opinion, and issues with certain governments. As with all financial instruments, the value of a given cryptocurrency is a perceived value in what the seller is willing to trade for that price.