Question: How can I convert Bitcoin to USD, EUR or other currencies?
To convert Bitcoin (or any other Crypto-currencies) to USD, EUR or other national currencies, you need to find a buyer of your Bitcoin first.
The buyer who is willing to exchange his/her fund with your Bitcoin would be your counter party.
Doing this through Crypto-Exchanges is a very easy way.
Normally a Crypto-Exchange offers you a number of exchanging methods and currencies to choose.
You can find the list of Crypto-Exchanges from here.
Bitcoin is a complete digital money which only exists online. Thus you must convert your Bitcoin in order to cash out.