Stock trading refers to the buying and selling of shares in a particular company. If you own a stock it means that you own a piece of the company. The stocks issued by companies can be traded in the secondary market once it is listed on the stock exchanges. The process of buying and selling of stocks is done by the brokers. Different stock brokers buy/sell stocks in the exchange on behalf of the investor. Once the broker passes buy order to the exchange, the stock exchange searches for a sell order for the same share. Once a seller and a buyer are found and fixed, a price is agreed to finalize the transaction.