I do not own pets as of now, but I'm interested. I read that dogs should be walked at best twice a day, but I was wondering where the cats get their exercise. Do they need any?
To exercise cats, play with them. Give them something to pounce and chase like a laser-pointer dot or a string or a light ball or a feather wand. Give them climbing/jumping opportunities -- all the better if the jump is a bit challenging but is rewarded with a good resting/watching spot or a view out a window. My two, siblings, sometimes like to wrestle or chase each other around the house.
Remember that they're taking a pretty good jump for their size every time they leap onto a chair or your lap. Simply living in a human household gives them some exercise.