Jack on fire delivering memorable tune (6)
I believe the answer is:
jingle
'memorable tune' is the definition.
'jingle' can be an answer for 'tune' (I have seen 'Catchy tune ' mean 'jingle' so perhaps 'tune' could also mean 'jingle'). I am not sure about the 'memorable' bit.
'jack on fire' is the wordplay.
'jack' becomes 'J' (playing card abbreviation).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'fire' becomes 'ingle' (ingle means a fireplace).
'j'+'ingle'='JINGLE'
'delivering' acts as a link.
Can you help me to learn more?
(Other definitions for jingle that I've seen before include "Catchy advertising tune - Pickwick Papers character" , "Short slogan" , "Catchy rhyme" , "Tune for advertisement" , "Metallic sound as of coins in pocket" .)