push pull amplifier (need explanation)

can someone please explain to me how this circuit works?especially the capacitor part at the squarewave input.(what is the capacitor and diode for)

Pls explain how the entire system works as well.

Thanks alot

I can't see that the circuit does anything useful. Are the Source of M13 and the (-) of the battery supposed to be connected to anything else?

ya the - is connected to the ground