TD Ameritrade was ranked #1 Online Broker 2020 by StockBrokers.com*. TD Ameritrade charges $0 for regular stock and ETF trades and is best known for its trading platform, thinkorswim, alongside its outstanding learning center for beginners. Alongside #1 Overall, TD Ameritrade received top awards for its trading tools, mobile apps, research, customer service, and education. Full review.
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.