For instance, the EUR/USD trading pair is the most traded currency pair in the world. Listed as EUR/USD makes the EUR the ‘base’ currency and USD the ‘counter.’ The price in the spot market next to this pair indicates the price of one Euro in USD. There will be a buy and a sell price, and the difference between the two is commonly referred to as the ‘spread.’
Cross Currency Pairs signifies secondary currencies traded against each other and not against the U.S. dollar. Examples include Euro vs. the Japanese Yen (EUR/JPY) or the British Pound vs. Swiss Franc (GBP/CHF). Most reputable brokers offer this category of trades, and it’s especially important for a forex trading account denominated in a currency other than the U.S. dollar, or for more advanced traders capitalizing on discrepancies between other economies.
Fluctuations in exchange rates are usually caused by actual monetary flows as well as by expectations of changes in monetary flows. These are caused by changes in gross domestic product (GDP) growth, inflation (purchasing power parity theory), interest rates (interest rate parity, Domestic Fisher effect, International Fisher effect), budget and trade deficits or surpluses, large cross-border M&A deals and other macroeconomic conditions. Major news is released publicly, often on scheduled dates, so many people have access to the same news at the same time. However, large banks have an important advantage; they can see their customers' order flow.

How much each pip is worth is called the "pip value." For any pair where the USD is listed second in the currency pair, the above-mentioned pip values apply. If the USD is listed first, the pip value may be slightly different. To find the pip value of the USD/CHF for example, divide the normal pip value (mentioned above) by the current USD/CHF exchange rate. For example, a micro lot is worth $0.10/0.9435 = $0.1060, where 0.9435 is the current price of the pair and subject to change. For JPY pairs (USD/JPY), go through this same process, but then multiply by 100. For a more detailed explanation, see Calculating Pip Value for Different Forex Pairs and Account Currencies.
The foreign exchange market is the most liquid financial market in the world. Traders include governments and central banks, commercial banks, other institutional investors and financial institutions, currency speculators, other commercial corporations, and individuals. According to the 2010 Triennial Central Bank Survey, coordinated by the Bank for International Settlements, average daily turnover was $3.98 trillion in April 2010 (compared to $1.7 trillion in 1998).[57] Of this $3.98 trillion, $1.5 trillion was spot transactions and $2.5 trillion was traded in outright forwards, swaps, and other derivatives.
Flights to quality: Unsettling international events can lead to a "flight-to-quality", a type of capital flight whereby investors move their assets to a perceived "safe haven". There will be a greater demand, thus a higher price, for currencies perceived as stronger over their relatively weaker counterparts. The US dollar, Swiss franc and gold have been traditional safe havens during times of political or economic uncertainty.[76]
Forex, also known as foreign exchange, FX or currency trading, is a decentralized global market where all the world's currencies trade. The forex market is the largest, most liquid market in the world with an average daily trading volume exceeding $5 trillion. All the world's combined stock markets don't even come close to this. But what does that mean to you? Take a closer look at forex trading and you may find some exciting trading opportunities unavailable with other investments.
For trading purposes, the first currency listed in the pair is always the directional currency on a forex price chart. If you pull up a chart of the EUR/USD, and the price is moving higher, it means the EUR is moving higher relative to the USD. If the price on the chart is falling, then the EUR is declining in value relative to the USD. The attached chart shows this. 
U.S. President Richard Nixon’s nullification of the Bretton Woods Accord in 1971 effectively ended the fixed price peg of the US Dollar — and by extension many other world currencies — to gold. The US Dollar officially became a floating fiat currency and was adopted as a reserve currency by many foreign nations, who continue to use it as a reserve currency today.

Some commonly traded forex pairs (known as ‘major’ pairs) are EUR/USD, USD/JPY and EUR/GBP, but it is also possible to trade many minor currencies (also known as ‘exotics’) such as the Mexican peso (MXN), the Polish zloty (PLN) or the Norwegian krone (NOK). As these currencies are not so frequently traded the market is less liquid and so the trading spread may be wider.

The need to exchange currencies is the primary reason why the forex market is the largest, most liquid financial market in the world. It dwarfs other markets in size, even the stock market, with an average traded value of around U.S. $2,000 billion per day. (The total volume changes all the time, but as of August 2012, the Bank for International Settlements (BIS) reported that the forex market traded in excess of U.S. $4.9 trillion per day.)