The nail should be cut from top to bottom, not side to side. The tip of the nail is placed in the hole in the trimmer and the handles are squeezed to advance the cutting blade through the nail. The cutting blade can be replaced when it is no longer sharp. You are less likely to cut into the quick if the cutting blade faces you. The cutting blade is closer to the quick when in this position The cutting blade is outlined in yellow.
Cats have a nail on the inner side of each foot called the dew claw.
Remember to trim these as they are not worn down when the cat scratches and can grow in a circle, growing into the foot. In this photograph the trimmer is being held in the reverse of previous photographs, with the handles pointing up instead of down. This is a matter of personal preference, what feels most comfortable to you. Also cut the dew claw from top to bottom rather than side to side. If the toenail is cut too short, you can use a styptic pencil containing silver nitrate to stop blood flow, although many animal object to this the styptic pencil as much, or more, than toenail cutting.