What I can do to a cat has fleas?

not my cat, but always comes to me and I take care of him for a year so can be taken as veterinarians is not mine …. but I'm really worried about what bad is their own do not bother, it's a shame! at least they could put within … "Chat … this cat? Oh, the cat of my aunt … she died and I took it …."

Cat Care: Fleas & Parasites : Symptoms of Heartworms in Cats