Mostly confused, learning English in it (2,7)
I believe the answer is:
in general
'mostly' is the definition.
(thesaurus)
'confused learning english in it' is the wordplay.
'confused' indicates an anagram.
'english' becomes 'e' (abbreviation).
'in it' indicates putting letters inside.
'learning' is an anagram of 'ingenral'.
'ingenral' enclosing 'e' is 'IN GENERAL'.
(Other definitions for in general that I've seen before include "Largely" , "on the whole" , "More-or-less" , "Where soldiers should have faith" , "Commonly" .)