In the futures market, futures contracts are bought and sold based upon a standard size and settlement date on public commodities markets, such as the Chicago Mercantile Exchange. In the U.S., the National Futures Association regulates the futures market. Futures contracts have specific details, including the number of units being traded, delivery and settlement dates, and minimum price increments that cannot be customized. The exchange acts as a counterpart to the trader, providing clearance and settlement.
The Aussie dollar is very dependent on the price of gold, as Australia is the 2nd largest gold producer in the world. If gold prices fall, this means Australia is getting less money for that gold, and generally the Aussie dollar will weaken in these circumstances. If gold prices rise this is great for Australia and their dollar will normally strengthen with the rise in the price of gold.
Since the market is made by each of the participating banks providing offers and bids for a particular currency, the market pricing mechanism is based on supply and demand. Because there are such large trade flows within the system, it is difficult for rogue traders to influence the price of a currency. This system helps create transparency in the market for investors with access to interbank dealing.