This is a time consuming process, but can be done if you are very patient.

Judge how close the cat will let you get before running off. Place a dish of wet food on the ground. Sit that distance from the food. Do not move. That means if you have an itch, don't scratch. Look to the side of the cat, not directly at it. And Wait! When the cat moves closer, don't move! Let the cat eat as much as it wants and just don't move! Let the cat leave when it's ready. Talk to the cat in a very calm, low voice.

Do this several days in a row, or even twice a day. Move the dish a little closer to your sitting spot every day. If you allow the cat to come to you, you will have better luck. When the food is within your arm's reach, it's very tempting to try to touch the cat. Don't. Keep moving the food closer until the dish is next to you. If the cat will eat this close to you, put you hand next to the dish when you first sit down. While the cat is eating, very, very slowly try to raise your hand. Move very slowly toward the cat's cheek, not the top of it's head. Once the cat allows you to touch it, you can move your hand to other places, but always slowly.

This can take several weeks if the cat is truly feral and you may not ever succeed. Other cats will respond quickly. A feral will not want to be picked up and attempting to do so can get you some bad scratches.

If you trap the cat, get it spayed/neutered and tested, then keep it in a room, you will increase your chances of taming the cat. But it still takes a lot of time and patience.

I have one feral that I haven't touched in the four years I've had her. A couple more that I've had a year or so will rub against my legs. They all 12 have run of the house but I don't attempt to pick them up.

Good Luck!