Kittens usually pick up on using the litterbox with minimal training. Make sure the box itself is shallow enough for the kitten to easily get in and out. And you want to start out with a non clumping litter like The Worlds Best litter. Sometimes all you need to do is show the kitten the box and they take it from there, but you may need to set the baby in it a few times a day right after a meal.
This is part of why I keep say to lock a kitten in one kitten proof room when they are wee babies/terrors. In my experience kittens learn best from watching adult cats use the litter box. I think the article covers everything. I have had luck demonstrating digging in the clean litter with 2 fingers and if necessary getting the kitten to dig a bit with their front paws. Like I said I had adult cats who taught my wee devils how to use a box. I only had to demonstrate to the orphaned babies once and then the other cats taught them the rest.
Take lots of pictures, they turn in to teen cats overnight