When one's all set, it goes into action (9)
I believe the answer is:
hairdrier
'into action' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'when one's all set it' is the wordplay.
I cannot really understand how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'set' could be 'hard' (similar in meaning) and 'hard' is found within the leftover letters.
This may be the basis of the clue (or it may be nonsense).
'goes' is the link.
Can you help me to learn more?