Why Does China Manipulate its own Currency?

China is not playing fair in the game of global trade, they are cheating other countries, companies, and consumers out of business by Manipulating their own currency.   So how does a nation like china control their currency? Can this actually be used to give an unfair advantage in global trade? If it can, why doesn’t every country do it? Can businesses profit from this man-made market failure? And does a currency price even matter?