My air conditioner is not working. I turn it on and I can hear the fan going downstairs where the furnace is. However, if I go outside where the air conditioner is, the fan is not going. What can I do?

I would check breaker at panel and the disconnect first, An AC tech will likely test for voltage to contactor, the 24 volts to contactor coil, then 240 out to fan and compressor.
Contactor will tell all.