There are 3 main systems for making nock point (also called nocking points) used but they only differ in the fact that that are made from different materials. The principles of how they work are the same. The purpose of a nock point is to give a constant place on your bow string onto nock your arrow.
Why is it important to nock your arrow at the same position on the bow string every time? There are 2 main reasons for this. The first reason is so you can have a consistency of shooting. If you nock too high your arrows will shoot low and if you nock too low you will shoot too high. It can also affect the angle at which the arrow impacts the target. The second reason is if you nock your arrow too low you will cut your bow hand with the arrow’s fletchings. This happens so very often and can be very easily avoided by having your nocking point set correctly.