We’re excited you want to learn about Bitcoin! Bitcoin is a digital currency (or cryptocurrency) which was designed to be sent via the internet. It was introduced in 2008 in a white paper published by an unknown person or group using the pseudonym, Satoshi Nakamoto. As explained in this white paper, there will only ever be 21 million bitcoins in existence (it has a limited and finite supply).
Bitcoins are created through a process called mining. Mining is done by miners (real people!) who use special computer software to solve mathematical problems. These people oversee the Bitcoin network, helping to confirm financial transactions (e.g. you sending Bitcoin to a friend), and creating new Bitcoins.
Miners are given small amounts of bitcoin as a reward for their work in helping to develop the digital currency. The entire process takes a lot time. To date, about 17 million bitcoins have been mined. As time goes on, they become harder and harder to mine.
This is because the calculations are getting more difficult and the job of mining has become very competitive.