centre frequency FC should be obvious from adjusting the sliders and listening. The tweeters come in around 2-3 kHz so above that you are playing with harmonics, below with fundamentals generally. Gain is the amount of boost or cut in decibels, Q is the resonance factor or spread of frequencies affected. The equaliser is parametric so you have control over the exact frequencies you want to program. You also have control of each part independant of each other in the mixer. Adjust how you like without getting overload distortion.