1) R4 is responsible for the amplifier bias, input impedance and forms a high-pass filter paired with C2
2) C2 protects the amplifier input from DC and is part of the filter.
3) R5 + VR1 / R6 is responsible for amplification. The lower the R5 value, the lower the minimum gain, the higher the VR1 value, the larger the operating range and the higher the maximum gain. The lower the R6 value, the greater the gain and vice versa.
4) C3 filters frequencies, the smaller the capacitance of the capacitor, the less low frequencies pass through, the nature of this ponder allows you to adjust the sound, more low frequencies, more phase and sag, less low frequencies, more toned sound and better readability, the attack is faster. For a clean boost, a large capacitor is better, for a heavy distortion, a small capacitor is better (unless, of course, you want to build a rat).
5) R7 limits clipping, the larger the resistor value, the less noticeable the clipping
6) C4, I'm not sure about its effect, but it doesn't cut high frequencies for sure, it affects clipping. Most likely, it limits at what frequencies the signal clips, or limits high or low.
7) C5 does the same as C2