High Pass filter will determine how much bass is running through the door speakers. 60hz will have more bass than 125hz on the high pass filter. It won't let any frequency below you set number run through the speaker. If u have a sub in your truck/car" turn this up to 100-125hz to take bass out of your mids and highs. It will keep your shit from blowing up
Low pass filter is vice versa. If your low pass is set at 40hz,no frequency ABOVE 40hz will be played through the speaker.
For sub control as in normal/reverse. If your sub is inverted, or upside down mounted on the box, then it's reverse. If the sub is mounted face up, with magnet inside box, then it's normal.
Lmk if u need anything else