Say you, in debt, appear first (5)
I believe the answer is:
debut
'appear first' is the definition.
'debut' can be an answer for 'appear' (thesaurus). I am unsure of the 'first' bit.
'say you in debt' is the wordplay.
'say you' becomes 'u' (I can't justify this - if you can you should believe this answer much more).
'in' means one lot of letters goes inside another.
'u' put within 'debt' is 'DEBUT'.
Can you help me to learn more?
(Other definitions for debut that I've seen before include "Initial appearance" , "Introduction" , "First attempt" , "First appearence as of society girl" , "First public appearance of performer" .)