As you can see from the video below, cats may take time to get used to wearing a harness.
The next step is to get your cat used to wearing the harness. Put it on the cat just before meal time so she will associate it with something positive. If your cat really doesn't like the harness, this might be a good time to give some special treats.
Once your cat is comfortable wearing the harness you can attach the leash. The great outdoors can be a scary place for a cat who has lived its whole life inside, so don't bring your cat outside until she is comfortably wearing the harness with the leash attached.
When you do venture outside together, hold onto your cat's leash- loud noises, dogs, or even other people may be frightening to your cat. Even if you are only going outside for a few minutes at a time, be sure your cat is up to date on all vaccinations and flea control.
With a little patience and some positive reinforcement, you'll be walking your cat in no time!