A door knob is a quite simple piece of equipment....very user friendly. They have been around for a very long time. Door knobs are nice. Use as follows:
Walk to a closed door.
Grasp hold of the rounded knob sticking out at about your waist.
Rotate your hand while simultaneously pushing the the knob forwards or backwards so that the door will slide open.
Step through the opening you have created and shut the door behind you.
Pat yourself on the back for the successful use of a door knob.