Thank you for giving a home to this cat.
You can give the cat free choice food right now, or follow the package directions for the cat food. Since it's a kitten, get "Kitten Chow" for growing cats; when you think the cat is about 1 year old, switch to an adult food.
Don't leave food out--this will draw skunks, mice, rats, possibly birds, possums and raccoons to your doorstep. And please don't expect the cat to chase away or prevent these animals from being around; the cat may catch or determine mice or other rodents, but they are not a good means of getting rid of them (and don't expect the cat to eat the mice/birds, etc.--unless the cat's mother taught it how to eat a mouse some of them can't figure out how to do it).
Definitely get your cat vaccinated, at the very minimum for rabies, and provide it with a place out of the rain--the garage or shed, or a waterproof box on the porch. If you can catch the cat, get it spayed or neutered. Otherwise, if it's female, you'll end up with a lot of kittens, or if it's male cat will will be wandering around searching for unspayed females to mate with (and be gone for days at a time). Google "low cost spay neuter" and your your county, town or area to see if there is a clinic near you that can do that for you.
You may also need to deworm the cat, even if it's staying outdoors; if you have kids or your dogs go outside, if the cat has worms, it can easily get passed on to your dogs or your family. (It's really pretty easy to do--pick some up at the pet store, and be sure to read the label).
I've found Dr. Foster & Smith's "pet education" website to be very helpful and would recommend you take a look at it. http://www.peteducation.com/