This is the carburetor of the Cessna 172.By moving the throttle lever from the cockpit, The position of the throttle valve change and the amount of the air goes into cylinders change.
On the other side, the throttle valve is connected to the accelerator pump which give more fuel when the air increased.
Carburetor is located at the bottom of the engine. Air comes in from the inlet through the filter, then airbox in which the carburetor heat valve is located, then go up into carburetor and mixed with fuel there then divided into 4 cylinders. Why bottom of the engine? Because it would be very hard to see the front over cowling if the carburetor is located on the top of the engine.
