A door handle whether it be a handle on a plate or a lever on a rose style handle, it controls the door by manipulation of a mortice latch (see item JL6666) – a mechanical fastener that joins two or more objects together...
The movement of the handle connecting spindle causes the attached bolt to be forced across the door's internal face, sliding in/out of the frame's latch face-plate allowing the door to be either opened or shut.