Carb again..

can anyone please explain to me the bahavior of the carb at normal speed and at idle state..
what happens exactly in the carb..
what changes at idle...

with the help of the figure shown in this link:
http://www.sweethaven02.com/Automotive01/fig0421.gif

help me understand this figure as well

the air comes in at the top, where it says venturi.
it then hits the throttle, which limits the amount of air that gets into the engine.
the rushing air then "pulls" out the gas, which is sitting in the float bowl.
the float bowl isnt labeled, but its the part that is shaded dark.
as the gas gets pulled out of the float, it is mixed with the rushing air and then goes into the intake manifold where it is pulled into the cylinders to be burned.

the idle port is a valve that allows only enough gas in to keep the engine idling. once the throttle is opened, the off-idle port takes over and allows more gas to be mixed
the idle mixture screw is what gats the mixture right in the engine.

idle mixture screw - http://www.chevyhiperformance.com/howto/45638/