Stock market is a centralized place, regulated by SEBI, that helps to trade shares. It can either be a primary market or a secondary market. Shares can also be subscribed via an IPO floated by the company direct. Shareholders can benefit via dividends, bonus announced by the companies. SENSEX & NIFTY indicates the top 30 & top 50 indices respectively and gives a sense of top performing shares to the shareholders and other markets globally. NSE gained more popularity by having provided more options,earlier on to traders.