If you really mean "invest" (which is serious, not playing), then I think that beginners and anyone with less than $25,000 to invest should go with a mutual fund (from a company like American Century, Fidelity, T.Rowe Price, Vanguard, etc.) or exchange traded fund (ETF) which is similar to a mutual fund except that it trades like a stock and is bought through a broker. I'd choose a fund that tracks a major market index like the S&P 500, Mid-Cap 400, or Russell 2000.

Doing that reduces your risk compared to buying an individual stock because the money is spread across many different companies and industries, so if one goes bad, you don't lose big.

While you're accumulating more money, study the market, read books, watch the ups and downs, learn what kinds of stocks do best under what economic conditions, and then when you have at least $25,000 (or preferably $50,000), I'd think about buying a diverse set of individual stocks in good companies. (Or you might not want to do all that work and just stick with the funds.)

The reason for the $25,000 or $50,000 limit is that with anything less than that, in order to diversify across 25 stocks you can only buy a small amount of each stock, which means the commissions will be too large a percentage of your investment.
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