Gain - Brilliant/Normal - these are the first stage gain controls in the circuit.
Think of them in parallel, like a vintage amp with jumpered inputs. The Normal side is thick and fat, the Brilliant side is bright with a tight bottom.
EQ - this equalizer is the same passive eq found on a HiWatt amp. I recommend starting with all controls at noon and adjusting to taste from there.
Vol - thes sets the overall volume of the pedal
Internal Trim Pot - This is the Power Gain control. Think of this as the master volume from an amp. Turn up for more power tube type of distortion