Bitcoin is a digital and global money system (currency). It allows people to send or receive money across the internet, even to someone they don't know or don't trust. Money can be exchanged without being linked to a real identity. The mathematical field of cryptography is the basis for Bitcoin's security.
You can make money by simply mining Bitcoin, or trading online via popular site such as Coinbase or bitstamp and other trading exchanges. Bitcoin has become very popular over the years, and it has jumped from $1,000 at start of 2017 to $19,000 by almost the end of 2017!