Plug the female end of your XLR cable into the male XLR output of your audio mixer. The XLR connection has the three pins that form a triangle. The female end has three holes that match the same triangle shape.
Plug the male end of your XLR cable into the female XLR connection on the back of your powered subwoofer that is labeled "sub input." The subwoofer will act as a crossover point and only play the low end of the music while it sends the rest of the frequency range up to your top boxes.
Adjust the crossover frequency knob located on the back of your powered sub. This allows you to select the point in the frequency range where the sub will begin to send the audio signal to your top speakers. Normal ranges for live audio applications are 60 Hertz to 120 Hertz.
Plug the female end of your other XLR cable into the "audio output" connection on the back of your subwoofer.
Plug the male end of your cable into the "audio input" connection in your top box. This will allow you to hear the full range of the music instead of just the low end.