I'm guessing the controls are for the gain (+ or - db) and the Xover (Hz) If not, then just pretend I am a little circus monkey throwing my poop at a midget.
The Gain affects how loud your speakers can get. If you set the gain to full, your speakers will get louder with each volume increase you make on the HU. If you set the gain to it's lowest setting, the volume will go up more slowly. I usually have it somewhere in the middle. Think of it this way. At full gain, you turn up the volume. Upon reaching 1/3 volume, it is too oud to listen to comfortably. At the low setting, you have more volume control from the HU, so you could more easily find a comfortablr listening level.
The Xover will block frequencies below what you set. If you set it to 80Hz, it will block any sound under 80Hz. This helps your door speakers since the don't have to play those frequencies so you get better sound out of them.
Hope this helped!
