The first thing you need for training is a harness or walking jacket, made just for cats (not for small dogs) and a cat leash. Some people prefer a bungee-type cat leash, which is gentler should your cat lurch. Always attach the leash to the harness or jacket, never the collar. Make sure kitty is wearing a cat collar, and an ID tag, just in case she gets away from you.
Next you need to provide some gentle and patient cat training! The first step is to allow your cat to "own" the harness. Leave it out for at least a week, allowing your cat to sniff it, mark it, drag it around - whatever makes her comfortable. Then begin having your cat associate the harness with pleasure. Talk to her in a comforting voice as you try to slip it on. If she cooperates, praise her and give her something she loves, like a treat, a good petting or a toy. If she resists, give up and try training again later. Cat training can take weeks!
Once you've trained your cat to wear a harness, let her wear it for very short periods of time indoors, and make that time pleasurable.
Let her own the leash as well. Eventually, attach the leash to the harness and let your cat get used to it inside. Give her a treat if she doesn't pull. If she does pull, stand still until she behaves. As soon as she stops pulling, give her a treat, or toy or whatever pleases her.
Once you train your cat to accept the walking gear, take her outside, where there will be no dogs or traffic or anything scary. If she's afraid, take her back inside. Your first outings should be brief. Don't expect to walk your cat like you would a dog (which also takes training!) Follow your cat's lead and let her get used to the idea.
If you get the knack of training her, and your cat likes walking on a leash, you may be able to take her on a real walk down a sidewalk on a quiet street and get some exercise. And if your cat loves it, walking on a leash may be something she insists upon. Daily.
Is your cat trained to walk on a leash?