The process is really simple.
First, use a cast iron dutch oven or other heavy pot. Put about 2 - 3 inches of peanut oil in the pot. On high heat, bring the oil up to about 375 degrees. If it is the right temperature, a little fish fri put in the pan will sizzle
Prepare the fish so that the fillets are thin - no thicker than 1/4 - 1/2 inch. Make sure that the fish is moist but not overly wet. Then dredge fish in fish fri. We usually do this by putting about 3 or 4 pieces in a tupperware container filled with fish fri. Shake the container. Place the fish in the oil - do not crowd. Let the fish brown to a light color (about 2 - 3 minutes at most) and turn to brown other side. The fish will float as it gets done. Do not overcook as this will cause the fish to be tough and rubbery.
We also fry shrimp the same way. Shrimp should be large 20 - 30 count per pound. Cooking times are shorter on shrimp so remove when light tan or brown.