When you buy stock in a company that is publicly traded, you are purchasing ownership shares in that business. As a stockholder, you share the value and the risk of that company.
Common stock is sold initially by a corporation and then traded among investors.
Common stockholders have voting rights. Preferred stock generally carries no voting rights. Most investment professionals consider stocks a great way to build value over the long term. In most years they have beaten the rate of inflation, often by wide margins. The 1990's, and the last five years in particular, have been unusually great years to be invested in large blue chip companies and high growth high technology companies.