When buying and selling in the forex currency trading system market, you'll see that there are four "currency pairs" that dominate the percentage of trades. Those four are the Euro vs U.S. Dollar, US Dollar vs Japanese Yen, US Dollar vs Swiss Franc, and US Dollar vs British Pound.

The goal when investing in currency is to be holding a currency that appreciates in value in relation to the other currencies. To use an overly simplistic example, if you bought 50 British Pounds for 100 US Dollars, held the Pounds for 1 week, and in that period the value of Pounds increased in relation to US Dollars, you could then convert those Pounds back into dollars for, say, $120.

Unlike the domestic stock markets, the forex currency trading is open for trades 24 hours a day. Much like the phrase "it's always noon somewhere," it's always business hours at some region of the globe. Since every country trades on the FX market, and it's open all day, the daily volume is roughly $1.2 trillion, which dwarfs that of the NYSE. Another comparison to make in order to truly realize the magnitude of the forex market is with the currency futures market (which has around 1% of the daily volume).

One other important distinction to make is that forex currency trading is not centered on an exchange like the NYSE or NASDAQ. There is no central body or organization required to act as middleman. Trading circulates between major banking centers around the world.

Until recently, there were strict financial requirements and massive minimum transaction sizes which prevented individual investors from trading. But with the advent of the internet came the FX brokers. A forex currency broker is similar to an online stock trading account such as etrade.