What is the function of the capacitor placement in the circuit?

C1 is for dc blocking, C3 and C4 are filter capacitors for the power supply, and C2 is a feedback capacitor. The magnification of this op amp design is so large that it only addresses the role of the capacitor you mentioned.

This is an active bandpass filter; 2. "Why should the resistor and capacitor be placed like this", the resistor and capacitor are set according to your passband center frequency, magnification, and quality factors, which can be determined by the column transfer function Calculation, this is more troublesome, some books have special calculation formulas, I usually use filter design software to get directly. 3. D1 and D2 in the figure are for limiting; 4. There is a problem with the power supply of your circuit diagram, which should be ±5V instead of two 5V; 5. The magnification of your filter is very large, and this op amp The bandwidth is relatively small, so this design is a bit unreasonable.

It feels like a comparison circuit, but it has a limited amplitude. C1 is a DC block. Only the AC component can be painful. d1d2 clamps the maximum value of the passed AC component to the voltage drop of the diode. The output should be a square wave.