How the USA equity & derivatives exchanges work?

It was quite a revelation when i came to know that in US market the brokers fulfil the orders & not the exchanges. Although I did some digging, the information is all one sided.

Require inputs from professionals who have traded in US equity as well as derivatives. If someone knows the order flow architecture, please share that as well.


Maybe this can help.

I still have no clue how the payment for order flow really exists. Wont there be arbitrage?

That’s what they’re making money with.