Game-
A neck harness is a strap you attach to your head that allows plates to be hung off it.You move your neck in the 4-directions(left,right,front,back)
The hammer 4-way neck machine allows the same type of movement except the machine takes the place of the harness.
Static holds against a wall-you lean towards a wall either facing it or with your back to it and brace yourself using your neck muscles.
Using plates-lie down on a bench face down or supine,put a plate on the forehead or back of the head(depending on which way you are laying) and raise your head upward.
The only people that will really benefit from direct neck work are those involved in contact sports(football,hockey,martial arts,boxing) who have reason to strengthen and/or injury-proof the neck.