"In simple terms Stock Exchange is an entity where the stocks and other securities are traded."In order for a firms stock to be traded in stock market, the company has to be listed in the stock exchange and follow other rules and guidelines of the exchanges where they are listed.
LISTING??????????
Listing means admission of securities to dealings on a recognised stock exchange. The securities may be of any public limited company, Central or State Government, and other financial institutions, etc.
Once a company is listed then the it has to disclose all the informations regarding their operations and financial details on a regular basis as per the guidelines of the exchanges.
WHY DO COMPANIES WANT TO LIST IN STOCK EXCHANGES??????????
The major reason for companies to list in stock exchanges is to Generate funds for future operations/expansions of the firm etc. When an investor buys the shares of such companies he becomes a shareholder and claims ownership in that company. He can hold the shares of that company as long as he wants or can sell the shares in the secondary market and liquidate his holdings.