You just want to feed goldfish a pinch of food and one time a day is enough if there is only one gold fish in the tank. If the fish doesn't eat all of the food within a couple minutes then you are giving it too much.
Less than you think! No matter how bug eyed they look at you :) Just a pinch a day but it depends on the size of the tank and the number of fish. Ask your local pet store owner if you want to play it safe.