Since your cat has never gone to the bathroom in a litter pan before, he most likely has no idea what it is. I'd suggest taking some of his feces and placing it in the pan, then showing it to him, so he realizes what it's there for. You must have a regular feeding schedule all ready set up, correct? If not, do so. Take note of how long it takes for your cat to eliminate waste after he eats. If you notice that he eliminates in certain spots, place the litter box near one of them. Once you know about how long it takes for the food/water to pass through, call your cat to you before the time comes, and get him interested in the litter box. Place him in it, if necessary, and reward him for being in there. Even if he doesn't have to go to the bathroom, get him used to the box periodically throughout the day, and reward him either with a treat, or a cuddle. Good luck!