What is the structure of crossbows?

In the crossbow machine, the one perpendicular to the back of the bow is called the lever machine. There is a tenon pin at the end of the lever machine, which is convex and mainly used to hang the drawn bowstring. The tenon pin can move up and down, and the wooden component at its lower part is connected with the trigger. The trigger is pulled back to drive the assembly to pull forward, so that the tenon pin is pulled down, the bowstring comes out and the arrow is shot out.

This is the basic principle. I can't find the picture. I read it from a book that specializes in ancient weapons.

How good is it? The early artificial crossbow can reach 300 steps, which is about 100- 150 meters. China's crossbow in Tang and Song Dynasties can shoot 3-5 arrows at a time, which can penetrate leather armor and thin armor.