Cats are naturally driven to periodically hook their front claws into suitable surfaces and pull backwards, in order to clean the claws and remove the worn outer sheath as well as exercise and stretch their muscles. This scratching behavior seems enjoyable to the cat, and even declawed cats will go through elaborate scratching routines with every evidence of great satisfaction, despite the total lack of results.

Indoor cats benefit from being provided with a scratching post so that they are less likely to use carpet or furniture which they can easily ruin.
Commercial scratching posts typically are covered in carpeting or upholstery, but some authorities advise against this practice, as not making it clear to the cat which surfaces are permissible and which are not; they suggest using a plain wooden surface, or reversing the carpeting on the posts so that the rougher texture of the carpet backing is a more attractive alternative to the cat than the floor covering. Some indoor cats, however, especially those that were taken as kittens from feral colonies, may not understand the concept of a scratching post, and as a result will ignore it.
Although scratching can serve cats to keep their claws from growing excessively long, their nails can be trimmed if necessary, with a small nail trimmer designed for humans, a small pair of electrician’s diagonal cutting pliers, or a guillotine type cutter specifically designed for animal nail trimming. Care must always be taken to avoid cutting the quick of the claw, analogous to cutting into the tip of a finger and equally painful and bloody. The position of the quick can be easily seen through the translucent nail of a cat with light colored claws but not in cats with dark colored nails, who therefore require carefully trimming of only small amounts from the nails.