They usually begin their journey of learning how to use the litter box at age 3 or 4 weeks. Naturally, one of their first instincts would be to watch their mother do it and then pick up on how they’ve seen it done. It is by instinct, too, that they begin to show motions of digging up when they feel like eliminating.
So, you don’t really have to train kitties on the process of using the litter box in the same way you would a puppy. You just have to guide them into locating the litter box.