Put in stern, I work (6)
I believe the answer is:
insert
'put in' is the definition.
('insert' can be a synonym of 'put in')
'stern i work' is the wordplay.
'work' indicates anagramming the letters.
'stern'+'i'='sterni'
'sterni' is an anagram of 'INSERT'.
(Other definitions for insert that I've seen before include "Enclose" , "Place within, pages of a publication say" , "Place in between other things" , "Put something inside something else" , "Add in" .)