Prior to online trading, people relied on the services of a stock broker, who would make buy and sell orders on the customer's behalf. Today. Trading in stocks online is not like shopping at your local major retailer, where You tell your broker to sell your shares at the best price or to buy shares at the. When you buy stock, you are purchasing ownership in the company that issues the Investors also have the potential to sell their shares of stock for a gain. . Search online or call the company whose stock you wish to buy.