National stock exchange in short NSE is the place where to form a company you should get registration with NSE providing all the data of company means total capitol in number of shares value of each share, executive of the company, name of product, market, demand etc.
After that company share can be available for exchange means buy, sale shares, for that NSE registers share broker all over the country and through broker public can trade by registering with brokers Broker gives facility to trade, on-line trading for that you have to down load software.
And you can trade through phone also.For trading you require to deposit margin money for day trading you require less margin then if you want to keep your transaction for more than one day you have to pay more margin.
You can do different types of trading means trading in company share, trading in indices(nifty), option trading etc.If market goes up index(Nifty) goes up and if market goes down index come down, means it represent national financial health.Stock exchange must for every nation without that nation can not survive.