maybe even a quick explanation of what they mean

 

Start by reading the manual that came with the unit. Most of these are for fine-tuning purposes and you don't need to worry about them just to hear something.

This amp appears to be designed specifically to drive subwoofers, with a pass thru for another amp to drive one set of speakers. If you have a higher end head unit designed for subwoofers, you can make almost all adjustments there. In that case I'd set the dials on the amp as follows:

Gain : halfway
Phase : zero
Subsonic: 20
Low pass: 250
Bass Boost: zero

This sets it up so basically the subwoofer will just get whatever comes out of the head unit's sub outs, the amp will work about like a conventional amp with no controls on it other than gain.

Now if you want to use the crossover feature it gets more complicated.