R2 is used to apply voltage to the microphone so that it can work normally. After receiving the audio, R2 outputs a signal to VT, which triggers the IC circuit.
R5 is used to form a loop with the photoresistor RG, so that RG can output different voltages to IC after exposure, so that IC can judge whether it should be triggered.
The function of R6 is to divide the voltage in series with R 1. Without R6, wouldn't the voltage on the integrated circuit be very high?