A Brief History Of The Stock Market A stock is a legal symbol of ownership in a business. When you buy stock, you are actually buying part-ownership of the business. In other words, you become a shareholder. A business will typically spread ownership to hundreds or even thousands of shareholders. Shares are sold when the company wishes to get cash. In a small business, it may be said that the owner has 100% of all shares. However, when a business grows beyond a certain size, it may require capital for expansion and selling shares is the easiest way to do that.