The most important things when caring for feral cats is to offer them food, fresh water and shelter, and, of course, to have them neutered to avoid them from breeding constantly.
Contrarily to popular belief, a well-fed feral and neutered feral cat will be a better hunter. It is thus important to feed feral cats with complete cat food as a healthy cat will have more strength. They may not find the food they need in the wild and will rapidly deteriorate. They should also have access to fresh water, which should be preferred to milk as cats are lactose intolerant.
Although cats might find shelter in a shed, they may need more warmth during cold weather, especially kittens, who are less resistant. Community Cats Network has designed some feral cat homes that are available to purchase.