Cut energy usage, said at first by them (6)
I believe the answer is:
greens
'them' is the definition.
I can't tell whether this definition defines the answer.
'cut energy usage said at first' is the wordplay.
'cut' means to remove the last letter.
'usage' is an anagram indicator.
'at first' suggests taking the first letters.
The first letter of 'said' is 's'.
'energy' with its last letter taken off is 'energ'.
'energ' anagrammed gives 'green'.
'green'+'s'='GREENS'
'by' is the link.
Can you help me to learn more?
(Other definitions for greens that I've seen before include "You may be putting on these" , "party politicians" , "Leafy vegetables" , "Vegetables (found on golf courses?)" , "Cabbage, sprouts etc" .)