A Bitcoin has a pre-determined amount of coins that it will produce. For example, the market cap for Bitcoin will be 21 million coins. Some amount of these coins are released at the start of the Bitcoin. The rest will be released using miners.
Miners:
In Bitcoin, you send some amount of your money to others and others will send you some coins as well. To facilitate this exchange, make sure that the transactions are secure and to confirm the record of movements of the coins, miners are used. Miners are simply computers that do calculations for the currency which verify and allow the secure movement of coins from one person to another. This computers then get awarded for their work by getting paid in Bitcoins. To pay these miners, new Bitcoin is "printed" and given to the miners. Like this, more and more coins get added until the Currency reaches its market cap. Then, miners are awarded money through transaction fees.