Litter training can only be done if the pig wants to be potty trained, and most of the time even when they are, they aren't 100% litter trained. To do so, your pig has to use certain corner(s) and when you find out what corner(s) those are you put litter box(es) in those corner(s). To help, you can have a kitchen, where you have shavings and that is where all the hay, food and water is, or you can have trays under the hay rack(s), and water bottle(s) and in one of those trays is where they are fed their daily pellets, and veggies, or just trays under the water bottle(s) and hay rack(s) as well as a kitchen or just a kitchen.
http://www.guineapigcages.com/forum/...-training.html