How do you hook up subwoofers in a car?

you need an amplifier first. decide where you want the amp, and wire it to that point. (amp comes with instructions for the wiring) once the amp is wired in, wire it to the radio(instructions come with amp) and screw it in. then locate where you want the sub(s) and wire it to that from the amp. almost all your instructions for installing subwoofers comes with the amp.