Maybe it's covered in spilt fuel, thus useless (6)
I believe the answer is:
futile
'thus useless' is the definition.
'futile' can be an answer for 'useless' (similar in meaning). I am unsure of the 'thus' bit.
'maybe it's covered in spilt fuel' is the wordplay.
'maybe' is an anagram indicator.
'covered in' means one lot of letters goes inside another.
'spilt' indicates an anagram.
'it' is an anagram of 'ti'.
'fuel' with letters rearranged gives 'fule'.
'ti' going into 'fule' is 'FUTILE'.
Can you help me to learn more?
(Other definitions for futile that I've seen before include "Ineffective" , "Useless, a waste of effort" , "In vain, a waste of time" , "Effectless" , "Useless or vain" .)