Fool it's silly to help (6)
I believe the answer is:
assist
'help' is the definition.
(assisting is a kind of helping)
'fool it's silly' is the wordplay.
'fool' becomes 'ass' (ass is a kind of fool).
'silly' is an anagram indicator.
'its' anagrammed gives 'ist'.
'ass'+'ist'='ASSIST'
'to' is the link.
(Other definitions for assist that I've seen before include "Give a hand to" , "Pitch in" , "Give aid" , "Work as a subordinate" , "Serve" .)