What to do with moldy food?

According to USDA: Food safety and Inspection Service, U.S. Department of Agriculture, although some molds are edible, some of them cause allergic reactions and respiratory problems, and some produce toxins under the right conditions that can make humans sick; So what should we do with moldy food? When we see mold on food, should we remove only the moldy part and eat the rest or throw that food away completely? To find the answer to this question, we need to know where the molds come from.