Just a newbie question, but for example, how does an ETF like FAZ, FAS or UNG create new shares? From what I gather, the price of the ETF is always reflected by the price of the underlying index, not by the buy-sell demand of the people who are trading the stock. So how does that work? Does the ETF create and destroy shares on the fly? How do they get the underlying futures contracts of shares so quickly in order to handle this? Is there some place that has that kind of info that describes this? Thanks in advance!