The foreign exchange market is where currencies are traded. Currencies are important to most people around the world, whether they realize it or not, because currencies need to be exchanged in order to conduct foreign trade and business. If you are living in the U.S. and want to buy cheese from France, either you or the company that you buy the cheese from has to pay the French for the cheese in euros (EUR). This means that the U.S. importer would have to exchange the equivalent value of U.S. dollars (USD) into euros. The same goes for traveling. A French tourist in Egypt can't pay in euros to see the pyramids because it's not the locally accepted currency. As such, the tourist has to exchange the euros for the local currency, in this case the Egyptian pound, at the current exchange rate.
For instance, if you opened a long trade on the GBP/USD currency pair, and the pair increased in value, the price limit at which the trade should close (the stop loss) would climb alongside the price of the currency pair. If the value of the GBP/USD then started to fall, the trade would be closed as soon as it hit your stop loss, preserving any profits you had made beforehand.
This information can then allow traders to make judgements regarding a currency pair's price movement. For example, if a Japanese candlestick closes near the highest price for the period, that would imply that there is a strong interest on the part of buyers for this currency pair during that time period. A trader might then decide to open a long trade to take advantage of that interest.
One unique aspect of this international market is that there is no central marketplace for foreign exchange. Rather, currency trading is conducted electronically over-the-counter (OTC), which means that all transactions occur via computer networks between traders around the world, rather than on one centralized exchange. The market is open 24 hours a day, five and a half days a week, and currencies are traded worldwide in the major financial centers of London, New York, Tokyo, Zurich, Frankfurt, Hong Kong, Singapore, Paris and Sydney—across almost every time zone. This means that when the trading day in the U.S. ends, the forex market begins anew in Tokyo and Hong Kong. As such, the forex market can be extremely active any time of the day, with price quotes changing constantly.