If you want to play the cornet in company, here's the music (8)
I believe the answer is:
concerto
'if you want to play' is the definition.
I can't tell whether this defines the answer.
'cornet in company here's the music' is the wordplay.
I cannot quite see how this works, but
an anagram of 'cornet' is 'oncert' which is located in the answer.
'company' could be 'co' (abbreviation) and 'co' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'the' is the link.
Can you help me to learn more?
(Other definitions for concerto that I've seen before include "Piece for soloist and orchestra" , "Orchestral composition" , "Work for orchestra and soloist(s)" , "Orchestral piece" , "Work for soloist and orchestra" .)