Where is the Crankshaft Position Sensor located?

I have limited car maintenance knowledge and have not been able to find anything on the internet to locate the crankshaft position sensor. Been working through suggestions for mechanic friends and the internet suggestions. The car would run rough sporadically, stutter, and die sometimes when at low speed or backing up. Symptoms have improved but still has died when backing. I am looking for any help I can get finding the sensor on the engine or other suggestions.