Trading forex involves making a profit from the fluctuations in the values of currencies from two countries. For a simplified illustration of how this works, let’s say that one British pound equals 50 Kenyan sterling (KES). You believe that the pound will strengthen against the KES, so you buy ten pounds for 500 KES. The exchange rate becomes one UK pound equals 75 KES, so if you sell your pounds you will get 750 KES, making a profit of 250 KES. Currencies are always traded in pairs, meaning that when you buy a currency, you are simultaneously selling another currency.
Currencies are traded in the foreign exchange markets. Unlike with stocks and other financial instruments there is no centralized exchange for trading forex, and thus, you can literally trade 24 hours a day since you can find a market that is open when you want to trade (although the market is closed on weekends, ending operations at 10pm GMT Friday and resuming at 10am GMT Monday).
You can trade currencies online using trading platforms that are provided by forex brokers. The platform not only allows you to place orders but also provides you with information such as price quotes that you would need to decide what trades you would make.