The ownership of companies is spread between many owners, and each owner owns a number of 'shares' in the company.  Some owners will own only a few shared, some will hold many.  As an example the National Australia Bank is a company and there are about 240,000 shareholders in the company.  National Australia Bank has a Share Registry [http://www.national.com.au/share/1949.htm] where the holdings are recorded so that you can see who are the shareholders in National Australia Bank, and how many shares each of them hold.    

The Stock Exchange provides a market place where brokers can meet together and buy and sell shares for their clients.  In Australia we have only one stock exchange, The Australian Stock Exchange [http://www.asx.com.au/].  The ASX was formed by combing the Stock Exchange of Melbourne, The Sydney Stock Exchange, and the Exchanges in Perth, Hobart, Adelaide and Brisbane.    

There is a page or two of financial news in your daily paper reporting what is happening in the stockmarket, and a huge list of prices of the shares each day.    

A Stockbroker is a guy that acts in the Stockmarket to buy or sell shares for an Investor.  There is a lot of discipline about the way that shares are bought and sold in the Stockmarket.  The Buyer has to be sure that when he has done a deal to buy shares the seller will deliver them reliably and on time.  And the Seller has to be sure that when he has done a deal to sell shares the buyer will be ready to pay for them when he delivers the shares.  For these reasons the only people that can operate in the Stockmarket, The Stock Exchange, are Stockbrokers.  And the Stock Exchange supervises the Stockbrokers to make sure that they are always able to honour their deals on time and expertly.   

In the day to day business of the Stockbroker the Stockbroker develops relationships with Investors and the Investors rely on the Stockbrokers to provide information and advice about what is happening in the market, and advice about what investments should be bought or sold.   

In the old days Stockbrokers were individuals and partnerships of individuals,  and the Stock Exchange was an association if individuals, a bit like a club.   Now Stockbrokers are companies, and the Stock Exchange is a company.  But the basic principles are the same - and a lot of the faces are the same.