[This post replaces an earlier one, which does not properly reflect modern banking practice.]
For most people the question of where money comes from is probably a bit mysterious, that is if the question ever even occurs to them. They might recall that notes and coins are produced at a mint, owned by the government. However notes and coins comprise only a small percentage of the money circulating in a modern economy. The rest exists only as accounting entries in banks and other places. In other words it exists only as numbers in computers. How does all this money come into existence?