A black and white pair of wires might be attached to the switch. Label and cover the black wire that has the power from the breaker. Also label and cover the white wire that permits the light to work. These are the power source.
Make sure the other two wires, black and white never have power to them. Use an ohmmeter or ringing tester between these two wires to see if the bell will ring or the meter will change when the switch is thrown. If so the black wire goes to the black wire, the white wire of the switch is taped as a black wire and goes to the light fixture copper screw, the other white wire (from the panel box) goes to the fixture silver screw. The green wire goes to the body screw of the light fixture. This introduces the switch before the fixture so the light can go on and off with the switch.