Some cats are polydactyl, and have up to seven claws on any paw. Normally there are four claws per paw, with one dewclaw on each of the front paws. If you have too much trouble holding the cat still for this, enlist someone else to help. You can then pick up a paw and go for it. Trimming claws should be done weekly.
Claws grow constantly, like human nails.
Unlike human nails, however, to stay sharp, claws must shed outer layers of nail. Cats will pull on their claws or scratch to remove these layers. This is perfectly normal and is comparable to humans cutting and filing their own nails. The sites are listed alphabetically, not due to the importance of their content. Instead, sponsor a needy cat at a cat sanctuary or shelter each month.