Chop the cabbage (green, purple of nappa) into thin strips and place it into a deep bowl (nesting bowls are perfect, use a larger of two)
Add the salt (and whey if using that) to the vegetable matter and mix it around so that each piece is covered. You can additionally add other flavorings like dill, garlic, mustard or other.
Place the smaller of the nesting bowls on top of the salted vegetables and press it down onto the veggies to press out the natural water within the veggies themselves. You may need to put a weight into the bowl.
If after 30 minutes your veggies are not submerged into their own brine than add up to 1 cup additional water (or add water just to lessen the saltiness). You can transfer the veggies to a ball jar with a weight or leave it in your nesting bowls. In either case it's important that the vegetable matter be submerged under the brine (salt water).
Ferment your kraut for 3 days or more days before transferring to cold storage. The longer you ferment the stronger the flavor. Cover tightly store in the fridge for consumption once you have the fermentation flavor you like.