What Influences Price?

Forex markets and prices are mainly influenced by international trade and investment flows. The Forex market is also influenced, but to a lesser extent, by the same factors that influence the equity and bond markets: economic and political conditions, especially interest rates, inflation, and political stability, or as if often the case, political instability. Though economic factors do have long term affects, it is often the immediate reaction that causes daily price volatility, which makes Forex trading very attractive to intra-day traders. Currency trading can offer investors another layer of diversification. Trading currencies can be viewed as a means to protect against adverse movements in the equity and bond markets, movements that of course also impact mutual funds. You should bear in mind that trading in the off-exchange foreign currency market is one of the riskiest forms of trading and you should only invest a small portion of your risk capital in this market.

What is Forex?

The off-exchange retail foreign currency market ("forex") describes the purchase of a particular currency from an individual or institution and the simultaneous sale of another currency at the equivalent value or current exchange rate. Essentially, the process of exchanging one currency for another is a simple trade based on the current rates of the two currencies involved.
At the core level of the world's need for money exchange is the international traveler. When traveling from the US to England, for example, you will of course need the local currency to pay for transportation, food, and so on. Upon arrival at the airport you will surrender (sell) your US Dollars in order to receive (buy) the equivalent in British Pounds. In this example, you sold the USD and bought the GBP, conversely the forex counter bought the USD and sold the GBP. The prices at which you buy and sell currencies are known as exchange rates. This rate or price fluctuates based on demand and on political and economic events surrounding each country's currency.

A Global Market

The example above illustrates foreign currency trading in basic terms as it relates to world travelers. However, the market is also utilized globally by each country's central bank (i.e., America's Federal Reserve), investment and commercial banks, fund management firms (mutual funds and hedge funds), major corporations, and individual investors or speculators. Depending on the timing of such transactions, purchasing a currency with the intent of later selling it at a better exchange rate (and vice versa) can potentially yield profits for investors, of course there is a strong potential for loss trading currencies as well.
Utilization by so many parties is why the Forex market is the world's largest financial market. This mind boggling volume is probably what led you to research the topic.

How do you access the market?

It is important to note that retail traders, such as yourself, will most likely be accessing the off-exchange foreign currency market (or Forex market) via an FCM (Futures Commissions Merchant) or broker. You will not be trading in the actual Interbank market itself. Your access to the total market will be determined by your chosen broker's limitations.
FCMs or brokers act as a bridge between you and their liquidity partner (sometimes larger global banks) that you would otherwise not have sufficient capital to do business with. ( view figure 1 ) The large majority of off-exchange retail foreign currency brokers act as market makers, meaning that by keeping many trades in house they create their own liquidity. Some retail brokers clear trades directly through to the larger banks that provide their liquidity. If you are new to the Forex market it would wise to research and understand your broker's particular business model and method of clearing trades.