Go to your belt tensioner, on the outside of the belt tensioner in a square hole. Insert your regular 3/8 ratchet in that hole and pull back the tensioner until you can get your belt off. Be sure to follow the drawing on your car to reinstall correctly. I usually draw one myself. Since you are there you may want to replace your belt tensioner if you have not done it in a while. It is held on by one bolt right thru the center of the base. 10 minutes tops. good luck.
You have to take the door apart
How to remove and install the serpentine belt on 1991 Chevy Blazer with AC?
1991 Corsica its under the trottle body
how to release serpentine belt tensioner on 1991 C1500 Chevy Silverado?
For a 1991 Chevrolet Corsica : My Chilton's Auto Repair Manual shows : ( 15.6 U.S. gallons )
Remove the wiring harness from the back of your 1991 Chevy Corsica turn signal. Remove the turn signal retaining bolts. The entire turn signal will come out. Reverse the process to install the new turn signal.
It doesn't have one, it is distributorless.
on the passenger side of the engine in along the serpentine ,between the power steering pump and the alternater . It is a wheel about 4 1/2 in. diameter with one 14mm bolt in the center.
13.6 gallons
a parts store
Green coolant (prestone, etc)
Depends on which engine it has. Try a Google Search.