Another important thing to consider is the distinction between investing and trading. When people talk about investing they generally mean the purchasing of assets to be held for a long period of time. These types of investments are usually made to reach a retirement goal or to put your money into assets that may grow faster than it would in a standard savings account accruing interest. Trading, on the other hand, most commonly involves the buying and selling of assets in short periods. Trading is generally considered riskier than investing.
A broker is simply a licensed person through whom you can buy and sell these stocks. When you use an online platform, it essentially acts as an online broker. If someone wants to buy any product, he can contact a brokerage service. They would place an order and let him know the market price of the product. If the investor is interested, they would include a commission for themselves and process the order forward. If the user wishes to buy stock, the broker would forward his order to a stock exchange, which would approximately take 3 days to complete including the money exchange between the broker and the investor.