Contain him to a small room, a bathroom, a laundry room, with no rug or anything that he can pee on. If you just took him in, it's best to confine him to a room anyway, because just letting him roam the house is frightening for him. Once he is in his "safe" room for a while, and knows nothing can get him, he'll calm down. I would say confine him to a bedroom, but if you aren't sure if he knows what to do in the litter box, you might not want to do that yet, maybe a bathroom would be better. How long have you had him inside? You can't force them. It's probably not that he doesn't know what to do in the litter box, it's probably because he's scared. Cats will hold their pee for an eternity when they are scared. Just make him feel safe and he'll probably go soon.