Cat with an ear infection?

So I found this stray cat in my garage, its a small tabby, and it has a really bad ear infection. I dont know what to do, but I dont want to leave it alone. Its either young/weak or old/frail, and has a very weak 'meow. It was kind enough that it came up to me and let me pet it, but it is still timid, so I dont want to have to do anything that might make it keep away from me. What could I do to help with the infection? Put anything in its food.. ? I really have no idea how to treat one.