Believe singer's after a drink for instructor (7)
I believe the answer is:
teacher
'instructor' is the definition.
(synonyms)
'believe singer's after a drink' is the wordplay.
'believe singer' becomes 'cher' (I can't justify this - if you can you should give a lot more credence to this answer).
'after' says to put letters next to each other.
'a drink' becomes 'tea' (tea is a kind of drink).
'cher' put after 'tea' is 'TEACHER'.
'for' is the link.
Can you help me to learn more?
(Other definitions for teacher that I've seen before include "Cheater (anag.)" , "Mentor" , "Lecturer" , "One who might give lines" , "Master" .)