Many online brokerages do not limit their customers to just online stock trading. Full-service brokerages offer banking services including checking accounts, savings accounts, credit cards, mortgages, and more with deposits of up to $250,000 backed by the FDIC. Bank of America (Merrill Edge) and Chase (Chase You Invest Trade) are two examples of banks that also offer online trading.
The trading products you can purchase using these platforms can include stocks, commodities, derivatives, bonds etc. which can be traded between the traders on the stock market with intermediates such as investment banks, stock exchanges, brokers and market makers. A communication network is set-up between the various intermediates and the traders, which facilitates proper execution of the whole system.