The fan is not working on my cental air conditioner unit outside... How do I get it working

You need to find the cause of the problem. If there's power to the fan, but the fan isn't turning (and if there's nothing else wrong), the fan motor will have to be replaced. They run around $100. You should also replace the motor's starting capacitor at the same time. They're cheap.

Check the capacitor first. This is a lot cheaper the a motor. Does the fan spinn freely by hand?