3. Get an education. Warren Buffett has suggested in the past that every investor should be able to understand basic accountancy principles, an annual report and stock market history. You probably do not need to become an accountant, but being able to understand the scoring system of the game can only help. There are thousands of books about investing and trading - you don't need to read them all, but you probably ought to read a few to enhance your theoretical knowledge.
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.