Need some carb help

[72gmcshorty]

I was looking at my carb (edelbrock 4 barrel) and noticed something odd (to me at least). When looking at the carb from the top, The carb has two back bowls (i think thats what they're called) exposed. The plate in front that opens and closes moves. My question is, what makes this plate move? I don't see it connected to anything. I see that the throttle has a little set screw that just touches the mechanism for moving the plate but when you step on the gas it moves away from the throttle plate thing. Anyone explain how this works or have a good pic? Please? This part in the pic. This is NOT my carb, just showing the part that I don't see hooked up to anything else on my carb