How Forex works and is it needed?

When it comes to stock market and exchange trading, first, what comes to mind for many people is forex. Really, advertising this type of investment (although such operations in this market can hardly be called) penetrated into many areas of our life - successful traders, who earn thousands of dollars in parallel with their main job or lying on the beach, look at us and from posters in subway cars, and from banners on the web. Meanwhile, everything is not so simple here.