Digital currencies created on a blockchain are known as cryptocurrencies. They uses strong cryptography technology.
There are today hundreds of different cryptocurrencies. You can buy and sell cryptocurrencies on cryptocurrency exchanges.
Bitcoin was the first cryptocurrency. Most cryptocurrencies are created on the blockchain technology.
The commonly known cryptocurrencies are public tradable assets. But there are instances where different types of cryptocurrencies can exist on more private based blockchains.
Essentially, cryptocurrencies are digital assets created on the blockchain with their own unique standards and specifications. You can buy cryptocurrencies at exchanges, get them through mining or staking.