It's used for drawing cold fish aboard (6)
I believe the answer is:
crayon
'it's used for drawing' is the definition.
I know that 'drawing' relates to this answer.
'cold fish aboard' is the wordplay.
'cold' becomes 'c' (eg on taps).
'fish' becomes 'ray' (ray is a kind of fish).
'aboard' becomes 'on'.
'c'+'ray'+'on'='CRAYON'
Can you help me to learn more?
(Other definitions for crayon that I've seen before include "Coloured rod" , "Stick to colour" , "Stick of coloured wax for drawing (6)" , "(Draw with) a coloured stick" , "Pencil of chalk or wax" .)