When you're making trades in the forex market, you're basically buying or selling the currency of a particular country. But there's no physical exchange of money from one hand to another. That's contrary to what happens at a foreign exchange kiosk—think of a tourist visiting Times Square in New York City from Japan. He may be converting his (physical) yen to actual U.S. dollar cash (and may be charged a commission fee to do so) so he can spend his money while he's traveling.
However, since the Forex market is a global market, it means there is always a part of the world that is awake and conducting business, and during these hours their currencies tend to experience the most movement. For example, currency pairs involving the US dollar experience the most movement during US business hours (16:00 to 24:00 GMT), while the Euro, Pound, Swiss Franc and other European currencies experience the most movement during European business hours, (8:00 and 16:00 GMT).
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.