Side mirror is useless
Go to a parking lot and find a car already parked all by it's self.
Position your car so that the other car is in your blind spot.
(usually this is somewhere a few feet behind your back bumper, and parallel with your car- blocked by the C pillar)
Adjust your passenger side mirror so you can see the car.
Note- you will likely NOT be able to see much of your car's quarter panel if at all. This is normal and a very common error most folks make when adjusting a non-OIMACTTA (objects in mirror are closer than they appear) mirror.