One of the most popular ways of studying stocks is called fundamental analysis. Investors who use this approach like to look at basic information about a company, such as the growth of its sales and profits, in an effort to figure out what they think is the true, or "fair," value of that company's stock. By comparing the current stock price to that fair value, you can determine if it might be a good time to buy that stock -- or if it's a stock to avoid like the Black Plague.
Some of the best-known investors in history have been fundamental analysts, including Peter Lynch, the legendary manager of the Fidelity Magellan mutual fund. Under his management, Magellan was the best performing mutual fund in history. Another famous fundamentalist is Warren Buffet, the brilliant investor behind Berkshire Hathaway. Berkshire Hathaway was once a textile company, but Buffet turned it into a vehicle in which he could invest in other stocks, with phenomenal success. A single share of Berkshire Hathaway now trades for over $60,000!
Most individual investors use fundamental analysis in some way to pick stocks for their portfolios. If you're looking for a way to build a "buy-and-hold" portfolio of stocks, made up of companies that you can purchase and then own for years without losing too much sleep at night, you'll probably use the methods of fundamental analysis.
Investors who use fundamental analysis usually focus on two separate approaches to picking stocks: growth or value (or sometimes a combination of both).