If you want to turn an outdoor cat into an indoor cat the first thing that you’ll have to do is teach him to use the litter box. This actually can be easier than you think. Cats are naturally inclined to go in sand or fine particles.  The first thing that you should do is confine your cat to a room with no absorbent surfaces other than his litter box.  Give him lots of attention and get some cat toys so that you could play with him as much as you can. When he starts to use the litter box regularly, give him more and more time outside of the room but make sure that you watch him closely.  Eventually, you will want to put another litter box in the place where you really want the box to stay. The location is key. Make sure that the box is in a quiet, easy to access place away from the cat’s food and water. Make sure that you wait for your cat to use the new litter box before you remove the first one.