They are illegal in some places, restricted in others, treated like dogs or cats in still others. They are obligate carnivores, which means that they must eat meat or meat products. Most people feed a ferret food or high-quality cat or kitten food. Quality in ferret food varies greatly. Avoid ones that include bits of fruit or veggies, these are okay as occasional treats, but not as a part of their staple food.
Many people also feed meats such as ground whole chicken, or mice.
There is much debate on how much diet and kibble foods which rely on grain for their form may contribute to health problems. Ferrets also imprint early on food, and it is not uncommon for them to refuse anything other than certain foods, even to the point of starving themselves to death. So it's a good idea to feed a variety of good foods from the start, in the event a company changes a formula or a food becomes no longer available. It is possible to get a ferret to adjust to a new food, but it can be a lot of work. They need both a high protein and a high fat diet.