I have never litter trained my pigs before (they're outside pigs), but I've heard about many people doing it succesfully! Put it in the corner where they do their business the most, and put a few of their poo poos in it, just so they get the drift! You can use normal cat litter, but only if they don't eat it, if they start eating it, then you'll have to switch to a product like feline pine, or wood shavings (not cedar or pine though!), or perhaps just normal guinea pig bedding!