Bitcoins is a form of crypto currency, a form of digital money. This is a digital money without a centralized bank. You can earn from it by mining whichh you will earn the small portion that is called Satoshi. There are lots of forms that are given at present like Dogecoin and Litecoin, but before, it is Satoshi. You will be given a free sites which you can mine satoshi for free. A timer will set and after 1 or 5 minutes, the site will refresh giving you a certain number of Satoshi to earn. It will be transfer to your balance that in return if you meet the minimum balance, you can transfer your balance to Bitcoin wallets in exchange for the currency depending on your country. This is created by Satoshi Nakamoto in 2009 and at present, it became one form of investment.