A note on the file provides understanding (5)
I believe the answer is:
grasp
'understanding' is the definition.
(I know that grasp is a type of understanding)
'a note on the file' is the wordplay.
'a note' becomes 'g' (musical note).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'the file' becomes 'rasp' (rasp is a kind of file).
'g'+'rasp'='GRASP'
'provides' is the link.
(Other definitions for grasp that I've seen before include "Seize firmly - or understand (5)" , "Firmly grip" , "Get hold of firmly" , "Catch on" , "Follow - understand - seize" .)