The number quoted for these prices is based on the current exchange rate of the currencies in the pair, or how much of the second currency you would get in exchange for one unit of the first currency (for instance, if 1 EUR could be exchanged for 1.68 USD, the bid and ask price would be on either side of this number). Learn more about Forex quotes in this article: Understanding and Reading Forex Quotes.
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.