How do i hook up a level line converter to the Head unit ( Radio )?

I need help on how to hook a level line converter to a stock radio i bought one today , and i dont know whare to hook the wires up to ???How do i hook up a level line converter to the Head unit ( Radio )?
depends on the car and if it has a factory amplifed system, but usually you can just tag it off the rear speaker output behind the deck. coloring varies from car to car, need more info for colors. or you can just grab it directly off the speakers in the car if you can get to them.