Sinatra does a turn for the Russian empress (7)
I believe the answer is:
tsarina
'russian empress' is the definition.
(I've seen this in another clue)
'sinatra does a turn for the' is the wordplay.
'sinatra does' becomes 'sari' (I can't justify this - if you can you should give a lot more credence to this answer).
'a' becomes 'an'.
'turn' shows that the letters should be reversed in order.
'for' means one lot of letters go next to another (I've seen this in other clues).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'an' back-to-front is 'na'.
'sari'+'na'='sarina'
'sarina' put after 't' is 'TSARINA'.
Can you help me to learn more?
(Other definitions for tsarina that I've seen before include "Wife of an old Russian emperor" , "top Russian women" , "Russian noblewoman" , "Russian empress (S, not Z)" , "Catherine, say" .)