Currencies are traded as pairs, and the movement of currency pairs measure the value of one currency against another. For instance, the EURUSD currency pair measures the value of the Euro against the US dollar. When the value of the pair increases, this means the value of the Euro has increased against the value of the US dollar. When the value of the pair decreases, this means the value of the US dollar has increased (or the value of the Euro has fallen).

With the expansion of retail brokers (which, of course, should always be regulated), the population size of intraday traders operating in a specific intraday time frame (M1-H1) determines the profitability of the trader trading this time frame. As the number of traders trading certain intraday time frames increases, conversely, the competition also increases, and the markets may become more efficient and easier to trade.
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.

International parity conditions: Relative purchasing power parity, interest rate parity, Domestic Fisher effect, International Fisher effect. Though to some extent the above theories provide logical explanation for the fluctuations in exchange rates, yet these theories falter as they are based on challengeable assumptions [e.g., free flow of goods, services and capital] which seldom hold true in the real world.
The main trading centers are London and New York City, though Tokyo, Hong Kong, and Singapore are all important centers as well. Banks throughout the world participate. Currency trading happens continuously throughout the day; as the Asian trading session ends, the European session begins, followed by the North American session and then back to the Asian session.
Economic numbers: While economic numbers can certainly reflect economic policy, some reports and numbers take on a talisman-like effect: the number itself becomes important to market psychology and may have an immediate impact on short-term market moves. "What to watch" can change over time. In recent years, for example, money supply, employment, trade balance figures and inflation numbers have all taken turns in the spotlight.
Due to Forex CFDs being leveraged, traders can access large portions of the currency market at a very low margin - sometimes as low as 1/500th of the size of the market they want to access (based on a leverage rate of 1:500). There are few additional costs as well - most Forex trading accounts have little (or no) commissions, order fees, and account management fees. If there are any trading fees, these are usually a markup the broker has added to the spread.
Forex is a portmanteau of foreign currency and exchange. Foreign exchange is the process of changing one currency into another currency for a variety of reasons, usually for commerce, trading, or tourism. According to a recent triennial report from the Bank for International Settlements (a global bank for national central banks), the average was more than $5.1 trillion in daily forex trading volume.