Begin to use file, for example, starting off prison escape nicely (4)
I believe the answer is:
open
'begin to use file for example' is the definition.
(as in opening a file on a computer)
'starting off prison escape nicely' is the wordplay.
'starting' indicates taking the first letters.
The initial letters of 'off prison escape nicely' is 'OPEN'.
(Other definitions for open that I've seen before include "Not enclosed" , "Honest - frank" , "Unrestricted; ready for business" , "Frank - unsettled" , "Start - frank" .)