Add or connect (6)
I believe the answer is:
attach
I believe this clue is a double definition.
'add' is the first definition.
(thesaurus)
'connect' is the second definition.
(I know that connect is a more specific form of the action enter)
(Other definitions for attach that I've seen before include "Append, join" , "Join, connect" , "Conjoin, tie to" , "Append, add on to" , "Affix, connect" .)