Small beside six-footer, a delivery-man (5)
I believe the answer is:
santa
'delivery-man' is the definition.
I can't judge whether this defines the answer.
'small beside six-footer a' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'beside' is a charade indicator (letters next to each other) (I've seen this in other clues).
'six footer' becomes 'ant'.
's'+'ant'+'a'='SANTA'
Can you help me to learn more?
(Other definitions for santa that I've seen before include "Midwinter gift bringer" , "-- Barbara" , "& 22 Father Christmas" , "generous visitor" , "He comes down chimney" .)