wanna make money?????

It can be destroyed - you can (if you wanted to, but it's illegal in most countries) burn paper currency, or melt down metal coins. And it does get made. The governments decide on how much currency should exist in the country, in order to change the cash flow - more is made so that more can be circulated, if the economy needs a boost. But if the government wants to slow down the economy to stop a "boom and bust" from happening, they will instruct banks to return a certain amount of currency to them. So you see, there isn't a set amount of currency around in the world - these levels are constantly fluctuating!