When you start your car and it screeches when starting up then the culprit is likely the serpentine belt being too loose.
Some cars contain one serpentine belt that drives the water pump, alternator, A/C compressor, power steering pump etc.
And some cars have two serpentine belts with one driving everything else and the other driving the A/C compressor.
If your car has two belts then it could be the A/C compressor serpentine belt and you can try turning off the A/C and if the screeching stops then it's the serpentine belt that drives the A/C compressor.
If it still screeches then it's the other serpentine belt causing the problem.
If your car has one serpentine belt then it's your serpentine belt getting stretched or your tensioner is not keeping your serpentine belt too tight.
Your serpentine belt needs the proper tension to keep it from slipping on the pulleys and if it's slips it will eventually break.
So get the serpentine belt checked out or replaced because if you break the serpentine belt you will be stranded and your water pump will cease working as well and your car could overheat leading to engine damage.