Cats don't need to be trained to use a litter box - they just do it.
By understanding why they prefer to eliminate in a litter box will help their human owners not to make any mistakes in having and maintaining the "cat box". It is a cat's basic instinct (even big cats) to eliminate away from their food and sleeping area and to bury the waste in order to hide their position from other animals and protect their nests and young.
Most kittens start using the litter-box at the age of 3-4 weeks on their own. At this young age you can show the kitten where to go and it might happen a bit faster:
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Here are a few things to consider about the litter box:
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