Cryptocurrencies are used in many ways.
You can send coins to anyone in the world.
You can buy some coins and hold them as an investment.
You can day trade with them and make profits.
You can then sell them.
You can mine them
Depending on where you live it will be more or less easy to turn your crypto coin into local currency. Some sites like Coinbase or coinberry will buy your BTC and now ETH and deposit the money in your account.
BTC is the bitcoin and ETH Ethereum are the easiest one to cash out they are widely accepted. But you can also use an exchange site to sell other coins for BTC that are easier to cash out.