Unlike dogs, you don't have to walk cats on a lead, although you can buy cat harnesses, and some people use them.
Most cats, however, given free access to the outdoors, will exercise themselves whilst hunting. It is also a good idea, particularly if your cat is confined indoors, to provide her with a selection of cat toys with which to play. Anything impregnated with catnip always goes down well .
Toys needn't be expensive, either. Cats love cardboard boxes with holes cut in, to sit in and peer out of.