They don't yell and shout anymore, those are old videos you see.

How exactly do each of the major stock exchanges in the U.S. work?

For the NYSE, what are all of those people yelling and shouting back and fourth doing? Who do they represent?

This is how I imagine it: individual investors call up a local broker who acts as a middle man between the investor and a buyer somewhere else around the world?

Also, when you trade stocks online, are they being traded through the NYSE?

What about the NASDAQ? If you're trading stocks online, are they being traded through the NASDAQ?

One last question, I noticed there are "company booths" on the floor of the NYSE. Does every listed company on the exchange have a personal booth? Or do only large companies (like Goldman Sachs) have booths on the floor?

Or do only the "market makers" have booths on the floor?

Thanks.