Well, if you look at it from a trading perspective, really big trades can move the market in a particular direction. If somebody buys a million shares of a company's stock it will most likely lead to a higher stock price in the future because somebody demanded them.
If you take a look at what the Federal Reserve, our central bank, is doing, they are throwing money at bad assets. The more money they print, the more supply of money exists, meaning that the value of those dollars decreases. It's just a matter of supply and demand.
If that's what the question is trying to get at...