Mining, or processing, keep the Bitcoin process secure by chronologically adding new transactions (or blocks) to the chain and keeping them in the queue. Blocks are chopped off as each transaction is finalized, codes decoded, and bitcoins passed or exchanged.
Miners can also generate new bitcoins by using special software to solve cryptographic problems. This provides a smart way to issue the currency and also provides an incentive for people to mine.
The reward is agreed-upon by everyone in the network but is generally 12.5 bitcoins as well as the fees paid by users sending transactions. To prevent inflation and to keep the system manageable, there can be no more than a fixed total number of 21 million bitcoins (or BTCs) in circulation by the year 2040, so the “puzzle” gets increasingly harder to solve.