Astute readers will realise that the above guidance is mainly taking different angles to help prepare for and guide decision making by the investor. The ability to confidently make decisions is vital for investment profits and long-term success. This pdf about the decision making models of Charlie Munger (business partner to Warren Buffett at Berkshire Hathaway - both are certified investment immortals) is almost certain to prove helpful.
In contrast to finding an expert or two that seems to make valuable and careful decisions, do your best to avoid listening to share market 'tips' from friends or work colleagues. Typically these people will know less than you and have very little to base their suggestion on. No matter how well meaning it may be, advice from someone who knows next to nothing about the topic in question is not advice.
For online platforms, websites give the user options and availability of the stock he wishes for, across all the platforms available. If he places an order, it gets stored in a database. After the confirmation of the trading account and payments, the order gets forwarded and the user gets his stock, in the form of money, transferred to his trading account.