Most of these services offer some form of free portfolio tracking - this enables you to create a portfolio and track it properly to see how you do with no money on the line. This used to be known as paper trading in the 'good old days' before 2001. This kind of exercise can be a good way to learn and play around with things without being either serious or costly.
A trading platform is software used for trading: opening, closing, and managing market positions through a financial intermediary such as an online broker. Online trading platforms are frequently offered by brokers either for free or at a discount rate in exchange for maintaining a funded account and/or making a specified number of trades per month. The best trading platforms offer a mix of robust features and low fees.
Then what? You might be new to investment but already wealthy, what do the super rich do to diversify? They use real estate in New York, London and the Cote d'Azure as a reserve currency. They change their country of residence to a tax haven, pursue naturalization through one of the EU citizenship by investment countries and then buy a sports franchise. Sorry, the sports franchise isn't actually an investment...
At the same time, there are literally hundreds of thousands of individuals who buy and sell corporate securities on one of the regulated stock exchanges or the NASDAQ regularly and are successful. A profitable outcome is not the result of luck, but the application of a few simple principles derived from the experiences of millions of investors over countless stock market cycles.
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.