Speaker-Level Input to RCA Cables Subwoofer Installaton?

Recently my friend gave me his old amp, because of this I sold my old amp because the new one is more powerful. When I first got my subwoofer I had it proffesionaly installed, the old amp had speaker-level input on it while the new amp does it, it only has an RCA input. How can I convert the speaker wire input cables into RCA cables. I have a Ford Edge and I am unframiliar and unsure how to install a line out converter with the touch screen head unit. If anyone knows of a good installer or would be able to install it for me for cheap please message me.

Subwoofer are those speakesrs which reproduce low notes and for installing in a car you will need a tool kit and 12-gauge wire to connect the subwoofer these are the basic things i know and for installation you should take it to any expert only.

lol^ just go down to walmart and pick up a cheap loc(line out converter). Tap low side of output in stock stereo. hook up rca's and enjoy