Stocks or shares or equities represent small units of ownership of publicly traded companies. They are sold to raise money to cover start-up costs or to expand the company. When you buy a share of a company, you are essentially buying into the company and own a part of the business and are entitled to a small fraction of the assets and earnings of that company.
Some of these companies, mostly long-established firms repay their stockholders by paying them yearly dividends, provided that it is making a profit. The rest are considered as growth stocks; the companies, usually new ones, reinvest all the profits it made during the year to fuel growth and/or expansion.