Share market is a place where people from all over the country can buy or sell shares. Nowadays tradings are done in online using (DEMAT A/C) .
NIFTY consists of top 50 actively trading companies from 24 different sectors. It is traded in NSE (National Stock Exchange).
SENSEX consisting of 30 stocks based on the total volume of stocks traded. It is traded in BSE (Bombay Stock Exchange).
If a public limited company wants huge capital they offer IPO (Initial Public Offer) to the public and it is conducted only once in the life time of the company.