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 really see how this works, but
'american' could be 'us' (United States) and 'us' is found within the answer.
an anagram of 'fuel' is 'eful' which is within the answer.
No letters remain.
This explanation may well be incorrect...
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" .)