Concertgoer's back inside, enthusiastic about opening musical piece (5)
I believe the answer is:
'opening musical piece' is the definition.
'intro' can be an answer for 'piece' (intro is a kind of piece). I am unsure of the 'opening musical' bit.
'concertgoer's back inside enthusiastic' is the wordplay.
'back' indicates one should take the final letters.
'inside' is an insertion indicator.
'enthusiastic' becomes 'into' (I've seen this before).
The final letter of 'concertgoer' is 'r'.
'r' inserted inside 'into' is 'INTRO'.
'about' is the link.
Can you help me to learn more?
(Other definitions for intro that I've seen before include "Prologue, opening (abbr.)" , "this may get one started" , "Start of work" , "Song's first few bars" , "One starts" .)