Handy American fuel product (6)
I believe the answer is:
useful
'handy' is the definition.
(I've seen this before)
'american fuel product' is the wordplay.
I cannot quite understand how this works, but
'american' could be 'us' (abbreviation for United States) and 'us' is found within the answer.
an anagram of 'fuel' is 'eful' which is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for useful that I've seen before include "Capable of serving some purpose" , "Handy, serviceable" , "Practicable" , "Make yourself . . . . . . - help out" , "Functional and worthwhile" .)