He's useful in the kitchen (5)
I believe the answer is:
basil
'he's' is the definition.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for basil that I've seen before include "Boy - herb" , "Herb (from Fawlty Towers?)" , "Saint" , "Aromatic herb with purplish-green leaves" , "Herb - boy's name" .)