Paint a girl and a boy (6)
I believe the answer is:
enamel
'paint' is the definition.
(I know that enamel is a type of paint)
'a girl and a boy' is the wordplay.
'a girl' becomes 'Mel' (short for Melanie).
'and' means one lot of letters go next to another.
'a boy' becomes 'ena' (I can't explain this - if you can you should believe this answer much more).
'mel' put after 'ena' is 'ENAMEL'.
Can you help me to learn more?
(Other definitions for enamel that I've seen before include "Dental material" , "hard stuff" , "Crown Protector?" , "protective coat" , "Outer tooth material" .)