mining bitcoin is the only way to increase the bitcoin supply, which is around 98% mined (from memory). Mining will supposedly finish close to the year 2140... at that time the miners reward would be only the transaction fee... but not really ( https://bitcoinmagazine.com/culture/bitcoin-is-time-traveling-energy ). When mining is complete it will be just under 21 million bitcoin and no more bitcoin will be produced.

At the moment 6.25 baby bitcoin are rewarded to the miner (or mining pool), that finds the special number to close the block that includes transactions; and also now some random java scrip and stupid jpgs, forever, I repeat, FOREVER, in the timechain.