Bridging is done one the amp, it is a matter of combining two channels into one for increased power. How the coils are wired into the amp determine the impedence load. The lower the impedence, the more power the amp will draw. For example, say your sub has dual 4 ohm coils, wiring these coils in parallel will drop the impedence in half or 2 ohms (+ to +, - to - on the coils). Yoy amp is probly a 2-channel and on the amp you will see a line pointing to a + and a - that says bridged, the + from the speaker goes to the + on the amp, the - to the negative on the amp. You will need to determine the specifics of your system and go from there. Do a search for a woofer wiring wizard on the net and you can input your specs and it will show you how to wire a system in parallel, series, etc to achieve the desired impedence load.