I have an outside switch to control a light in the garage. The white wires are connected in the box and there is one black and one red wire. How do I connect them to a single pole switch.
If this is the way you found it and you're sure there used to be a switch there, connect the black wire and the red wire to the two screw terminals on a single pole toggle switch.
If you're not sure, then remove the wire nut from the white wire and test for 120 Volts between the black wire and the white wires with a multi meter. Also check for voltage between the red wire and the white (there should be none). Trace the red wire to the garage light to verify it's for the light.
Turn the breaker on only when checking for voltages and leave it off when doing any work or mounting the switch into the box.