Use heat to bond metal and yellow dye (4)
I believe the answer is:
weld
'use heat to bond' is the definition.
I can't judge whether this definition defines the answer.
'metal and yellow dye' is the wordplay.
'metal' becomes 'W' (W is an example).
'and' means one lot of letters go next to another.
'yellow dye' becomes 'eld' (I am not sure about this - if you are sure you should believe this answer much more).
'w'+'eld'='WELD'
Can you help me to learn more?
(Other definitions for weld that I've seen before include "Solder" , "Join by fusion; dye plant" , "Join (metal) by melting" , "Fuse metal parts" , "Join; fuse" .)