Need Help With Op Amp Circuit Explanation

[Kimly]

I am a beginner Electronics enthusiastic and I am trying to build a circuit and I kind of know how to go about assembling the circuit but I do not understand purpose of some of components in the circuit. I have the schematic of the circuit below for your reference.

 

 

What is the purpose of the 6.8k resistor, 100 nF capacitor and 680k resistor?
What is the purpose of the combination of the 100 nF capacitor and 680k resistor in the first op-amp and 2nd op-amp?

What is the purpose of the combination of 1uF capacitor and 68k resistor?

Also note shown on this circuit, what is the purpose of a Comparator and how does it generate a square output pulse if attached to the two stage op-amp at IC2 pin 7?

Thank you So much.