Cryptocurrencie is a online currency of the world. Anybody can buy and sell the currency. There are no documents need to buy and sell. So anybody can use this coin.
The most popular online currency is : BTC, ETH, ETC LTC
The next level currency is : DOGE coin, Desh coin etc.
But if you look Coinmarket Camp, you can see some new coin Release online.
There are many token released on coinmarket. You can earn many token and exchange other cryptocurrency. This is the most unlimited earning way.
Airdrop are giving new token. This is the main way to earn very easily. But there are some fake airdrop. So be cearfull.
Coinmarket Camp help you to give full details of any coin.