It needs hint of lime when served up (5)
I believe the answer is:
salsa
'it needs hint of lime when served up' is the definition.
The definition suggests a singular noun which matches the answer.
'it needs hint of lime when served up' is the wordplay.
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
'needs' means one lot of letters go next to another.
'hint of' indicates taking the first letters (the smallest possible amount of the word).
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'served up' shows that the letters should be reversed in order (in a down clue, going upwards).
The initial letter of 'lime' is 'l'.
'as' reversed gives 'sa'.
'sa'+'l'+'sa'='SALSA'
Can you help me to learn more?
(Other definitions for salsa that I've seen before include "The Latin-American sound" , "Tomato relish" , "Latin-American dance" , "Spicy tomato sauce" , "Saucy dance" .)