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.
The world then decided to have fixed exchange rates that resulted in the U.S. dollar being the primary reserve currency and that it would be the only currency backed by gold, this is known as the ‘Bretton Woods System’ and it happened in 1944 (I know you super excited to know that). In 1971 the U.S. declared that it would no longer exchange gold for U.S. dollars that were held in foreign reserves, this marked the end of the Bretton Woods System.
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.