after being cut? Why on young puppies and not when older
Short version: you cut it according to the breed of dog and how you want the ear to look when it’s done, then you tape it in place until it heals and the cartilage “sets” in the desired position. You do it to puppies instead of adult dogs because the cartilage in their ears is still growing and has not “set” on its own yet.
A relative of mine had this done to their puppy. After the ears were cropped and bandaged, they were taped to a styrofoam cup that was lashed to the top of his head. He had to wear this contraption for a couple of weeks, as I recall.