Wiring dual 12" subs to mono amplifier? - what does a dual mono amplifier do

Recently, I have my girlfriend my JL Audio 12 "W3 subwoofers, she blew, NEXT, lol I went to buy her a new subwoofer, and chose a dual 12" JBL GTO side and explained that they worked well with mono amplifier. and my question is how the two submarine cables in my monkey-amplifier (downhill, 500 watts RMS). Thjere contains only positive input amplifier / negative, but it tells me that connect the two sets of positive and negative results of the subwoofer connected. Im not sure if I have a positive or negative amplifier to connect if I use a port of the amplifier, which cut two positive input to submarines, and vice versa with the negatives, please help resources!