If you take a look at the FOREX quotes on your trading platform you will see that there are two prices for each currency pair. One is the price at which you can buy, referred to as the "ask price", and the other is the price at which you can sell, referred to as the "bid price". The difference between these two prices is known as the spread. The ask price is always higher than the bid price.
The foreign exchange market is the "place" 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.