Open an account [deposit money] at a bank or other financial instituion. Most offer online trading but some you have to talk with a broker and they make the buy or sale for you.
But first......study the market, learn about trading and the cost involved with making a buy or sale. For starters.....
https://login.yahoo.com/config/login...quote&.intl=us
http://investing.money.msn.com/inves...arket-summary/
Investing in buying stock should be done in fairly large amount of money....otherwise the borkerage fees will take a big percentage of your money.
Learn as much about a company as you can.....before you buy it.
IMO....you should not be buying stocks if you only have say $ 1000 or $ 2000 to invest. But most investors normally start small and keep adding money to there account to invest more. An established investor should own 10 to 15 stocks [maybe even 20 stocks] and invest about the same amount in each of them.