Turn off the power to the switch. Flip the circuit breaker so that there is no power flowing on the line where you'll be wiring the switch.
Strip the wire on the black and white leads of your wiring. The switch interrupts the circuit, so you'll have one pair of wires (black and white) coming from the circuit breaker, and another pair leading to the light. Strip back the insulation from each set of wires so that you have 3/8 to 1/2 inch of wire on each of the white and black wires.
Attach one black wire to each of the screw terminals on the light switch. Tighten the screw down so that the wires are secure.
Attach the two white wires together with a wire nut.
Turn on the circuit breaker and test the operation of the switch. If it works properly, screw the switch into position in your gang box and place the cover over it.