Carol's turn in Act 1 bothered unbeliever (8)
I believe the answer is:
agnostic
'unbeliever' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'carol's turn in act 1 bothered' is the wordplay.
'carol' becomes 'song' (I've seen this in another clue).
'turn' says the letters should be written backwards.
'in' is an insertion indicator.
'1' becomes 'I' (Roman numeral).
'bothered' indicates anagramming the letters.
'song' back-to-front is 'gnos'.
'act'+'i'='acti'
'acti' with letters rearranged gives 'atic'.
'gnos' put into 'atic' is 'AGNOSTIC'.
Can you help me to learn more?
(Other definitions for agnostic that I've seen before include "Religious sceptic" , "Incredulous person" , "He finds it difficult to believe" , "One doubts" , "Doubter - coatings (anag)" .)