Look displeased when put out about nothing (4)
I believe the answer is:
pout
'look displeased' is the definition.
I can't judge whether this definition defines the answer.
'put out about nothing' is the wordplay.
'out' means one lot of letters goes inside another.
'about nothing' becomes 'o' (O resembles 0. I am not sure about the 'about' bit.).
'put' enclosing 'o' is 'POUT'.
'when' is the link.
Can you help me to learn more?
(Other definitions for pout that I've seen before include "Fish; expression" , "Push out the lips (alluringly?)" , "Sullen expression" , "prepare for selfie?" , "Look miffed" .)