Ask a Fool: How Do You Buy Stocks?
Most people buy their stocks through an online broker, such as TD Ameritrade, E*Trade, or Schwab, just to name a few. These all charge trading commissions under $10 and offer valuable educational resources for new and experienced investors. It's a good idea to shop around and compare the fees and features of a few brokers before picking one (The Motley Fool's broker center can help you with that).
Once you've decided, opening your account is pretty straightforward. You'll need to sign a few forms and answer some questions, which can generally be done entirely online, and you can fund the account via an electronic funds transfer (ETF) from a checking or savings account, wire transfer, by mailing in a check, or through a few other less-common methods.
After your account has been opened and funded, most brokers have a quick order-entry feature on your account's home screen. You'll be able to choose whether to enter a "limit" order, which means that you name the maximum price you're willing to pay for the stock, or a "market" order, which means that you want to buy shares now at the current market price.
Source: Fool.com