Forex is the market where tens of millions of people earn on the difference of currency prices. Some of them, such as George Soros, you, probably, have heard, but most are ordinary people with small capital.
Forex trading is not commodities, and currencies. One currency is bought and sold always in exchange for another. The Forex market is huge, it surpasses, for example, the global stock market dozens of times, and participate on it: Regular consumers (firms and individuals). For example, the retailer of Swiss watches in the US buy Swiss francs for us dollars to pay for the next consignment of goods from Switzerland, and Finnish phone maker Nokia, need to buy dollars for Euros to pay for new parts from the USA. Investors who buy foreign currency to buy shares in another country. For example, if the Bank City Bank to buy stock in European BMW, you first need our dollars to buy euros, and then euros to these European exchange to buy shares. Speculators, from the super-rich such as George Soros, to ordinary students, who trade on the fluctuations of currencies. Each currency in the forex market its designation. For example, Euro written as Eur and United States dollar is written as Usd. Because one currency is bought and sold always for another, the currency is denoted in two currencies. This is called a currency pair and is usually written through the line. For example, the Euro to US dollar (or the currency pair Euro-dollar) looks like Eur/Usd.