This is something that most cats seem to take to surprisingly easily if
they are simply restricted to an area indoors where a tray has been left.
If you are experiencing problems, you could try experimenting with different
types of commercial litter. You cat may have a preference for a certain type.
You could even try adding some earth from the yard, or garden, into the tray
to give it that authentic aroma your cat appreciates.
Make sure that the tray is positioned in a site with easy access for your
cat, yet in a spot that is reasonably secluded, as many cats feel vulnerable
when they perform in a tray, and may not use it if it has been placed in a
very exposed position. Some appreciate the privacy of a tray that is equipped
with a commodious cover.