Only a start, but you finish in debt (5)
I believe the answer is:
debut
'only a start' is the definition.
I can't tell whether this definition defines the answer.
'you finish in debt' is the wordplay.
'finish' indicates one should take the final letters.
'in' indicates putting letters inside.
The final letter of 'you' is 'u'.
'u' going within 'debt' is 'DEBUT'.
'but' is the link.
Can you help me to learn more?
(Other definitions for debut that I've seen before include "Introduction" , "opening" , "The coming out of a society girl" , "entrance" , "First appearance, coming out" .)