Leverage: Leverage is capital provided by a Forex broker to bolster their client's trading volume. For example, if you use a 1:10 rate of leverage and have $1,000 in your trading account, you can trade $10,000 worth of a currency pair. If the trade is successful, leverage will maximise your profits by a factor of 10. However, please note that leverage also multiplies your losses to the same degree, so it should be used with caution. If your account balance falls below $0, you may trigger a broker's negative balance protection settings (if trading with an ESMA regulated broker), which will result in the trade being closed. Fortunately, this means that your balance cannot move below $0, so you will not be in debt to the broker.
Forex banks, ECNs, and prime brokers offer NDF contracts, which are derivatives that have no real deliver-ability. NDFs are popular for currencies with restrictions such as the Argentinian peso. In fact, a forex hedger can only hedge such risks with NDFs, as currencies such as the Argentinian peso cannot be traded on open markets like major currencies.
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.