Stock trading takes place in stock markets where buyers and sellers are lined up and make their best deal.
Role of broker is to act as a liaison between the buyer/seller and stock exchange
Role of exchange is to coordinate the trading that happens in stock market
Role os SEBI (Securities and Exchange Board of India) is to regulate the stock trading that happens in various stock markets
Role of Govt is to appoint and monitor SEBI and it’s actions
Role of bank is to help participants maintain their DEMAT (DEMATerialized) account