Pick level just specify which object will be selected if you click on entity in the graphic viewer: the entity or the component containing clicked entity.
"I want to get x,y and z points when I click on graphics viewer."
There is a problem, that you need an additional information in order to convert two coordinates of the click position inside graphic viewer to three coordinate of the 3D vector. Such information can be: constant value of one coordinate, any surface e.g. surface of the solid, or other 3D geometry.