Manual (8)
'manual' is the definition.
(instruction manual)
This is the entire clue.
(Other definitions for handbook that I've seen before include "Manual, reference" , "companion" , "Guide" .)
(Other definitions for user that I've seen before include "Person employing something" , "One who exploits others" , "One taking advantage" , "Right long-established" , "One getting benefit from" .)