How IT works -- no longer understand it, mate? (9)
I believe the answer is:
digitally
'how it works' is the definition.
(IT or Information Technology works digitally)
'no longer understand it mate?' is the wordplay.
'no longer understand' becomes 'dig' ('dig' is an old-fashioned word for 'understand').
'mate?' becomes 'ally' (I've seen this before).
'dig'+'it'+'ally'='DIGITALLY'
(Other definitions for digitally that I've seen before include "using fingers" , "how PC works" , "employing electronic equipment?" .)