From the look of his eye he has a disease called popeye, which is a bacterial infection, the white stuff looks like fungus which can appear on a sick fish. He is very poorly. You will need a strong antibacterial and anti fungal medication. I dont keep these sort of fish so I am sorry I cannot advice on a medication.
White stuff do look like fungus. Goldfishes are susceptible to fungal infections if kept at a too warm water temperature. Cool your temps down a bit working slowly. Using malachite green as instructed can help prevent further infections but be wary that some fish medication can harm plants, shrimps and snails though. An oxytetracycline based fish medication maybe best used to combat bacterial and severe fungal growths but this should for last resort purposes only