Forex market is the most popular among other markets, but unlike stocks or commodities, forex trading is done between two parties involved in the transaction. Forex is run by a global network of central banks, commercial banks across four major centers in different time zones: London, New York, Sydney and Tokyo. As you can see, you are able to trade 24 h/ day since time zones cover each other.
You can trade Forex in many ways, they all operate in the same way: by buying and selling one currency for another at the same time. For a long time, forex trading was done by a broker, but nowadays, the online trading platforms have made it easy for anyone to trade from home, any asset you like, not only Forex.