The papers he puts into groups (6)
I believe the answer is:
sheets
'the papers' is the definition.
(sheet is a kind of paper)
'puts into groups' is the wordplay.
'puts' becomes 'he' (I can't explain this - if you can you should believe this answer much more).
'into' is an insertion indicator.
'groups' becomes 'sets' (I've seen this in other clues).
'he' put into 'sets' is 'SHEETS'.
'he' acts as a link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sheets that I've seen before include "Bed covers" , "Pieces of paper and bed linen" , "They get blanket coverage" , "Bed coverings for the sailor's ropes" , "Leaves" .)