Can anyone explain these "numbers" to me?

This is actually three numbers questions, concepts which I have never understood.
The first is “running numbers”. What? I hear it in movies and on crime shows; “He’s a numbers runner.” I saw a good example on Malcolm X where the people would say a three digit number to a guy, but it isn’t clear to me how a winner is determined. Some guy who does or does not write the numbers down, and later some number is somehow picked? What? Who makes money from this and how?
Second; craps. I see that on movies too, and all I’ve ever been able to determine is one guy throws dice and a bunch of other guys holler and give money back and forth. The guy collecting all the money seems to know who gets some back and who doesn’t, but I can never tell how.
Third; the Stock Exchange. It’s very confusing to me. The floor is crowded, they’re all hollering and performing some arcane acts that I can’t follow. Some guys point to others and write something down, the camera keeps panning to numbers going up or down on a board, and I can’t determine how they can keep track of who hollers what. I understand that purchases are being made, but how do they do it? If everyone on the floor is jumping up and down, how do they later know that they got what they were trying for? Then the buzzer sounds and it all stops.
Can anyone enlighten me on any of these mysterious activities?