How to level a kitchen floor?

If you're talking about a couple of small dips, there's a product called "Thin set" or "Floor leveler" that's more or less just mortar that will stick to wood sub flooring.
It will work well so long as the floor is stable. (ie: it doesn't feel springy when you step on it.)
If the floor is bouncy, you'll need to add some reinforcement and if it's off by an inch or more, you're out of luck unless you want to jack up the house and add columns footings and beams.