Before the world became a frighteningly complex place, money was simple. It's a commodity, like anything else. The conceit, the deal, if you like, is that we all accept that money can be exchanged for any other commodity.
So if the world only contained three bananas, three fish and three coins, and we all accepted these were of equal value, then you have a starting point. But if you make three more coins, then you need two coins to buy a fish. Because you can create infinite amounts of money, but other resources are limited. Then derivatives came along...
For a slightly more sensible, more complex, but excellent "Economics 101", which predicted and describes what's happened to the world economy in the last few years (and is very depressing if you buy the author's ideas in full) read this:
http://www.hedgefundletters.com/wp-content/uploads/2011/03/a-template-for-understanding.pdfAnd there's an interesting piece on the guy who wrote that article in the New Yorker this month:
http://goo.gl/h14hA