This is comparable to the difference between the nail attached to your skin and the part that grows beyond it. It will be painful to your cat and bleed everywhere. When in doubt, trim less of the nail. It will just mean trimming more often. Clip the portion above the quick for each nail and don't forget the dewclaws.
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.