content: Every transaction is broadcasted and checked against existing balances and such. A bunch of these updates are packed in a block. This block needs to be "encoded" (not actually what is happening but for ease sake ...) with some specific constraints. The network basically brute forces this encoding with random guesses and then checking their answer against a valid answer. This answer is then broadcasted and re-calculated by others. The person that found the answer first is awarded bitcoins for finding the answer. The amount you get decreases over time so there are a finite number of coins, and the difficulty of finding one increases as well.