You have an outside light that won't work but switch has power?

First and foremost make sure the light bulb is a good one. Try it in another fixture to make sure, even if it just came out of the box it was packed in. If you have checked the switch for power then you must have a tester. The power coming to the switch will most likely be on the top screw. Turn the switch on and see if you have voltage on the bottom screw. Check this voltage from the screws to the ground wire as the neutral will not be accessible in the back of the switch box. If there is voltage to the bottom screw then move on to the light fixture. Remove the outside light fixture and see if you get a voltage reading on the incoming hot (black ) wire. If there is voltage there then you have to see if the lamp holder is making continuity. If you have an ohm meter or a continuity meter remove the lamp fixture from the "hot" wire and the neutral connection and see if you get a reading across the fixtures black and white wire. This has to be tested with the bulb in the fixture. No continuity reading then there is trouble with the socket. Might be time to think about a new fixture.