Turns up, it's about charge for finishing order in joint (6)
I believe the answer is:
reefer
'joint' is the definition.
('reefer' can be a synonym of 'joint')
'turns up it's about charge for finishing order' is the wordplay.
'turns up' shows that the letters should be reversed in order.
'it's about' becomes 're' (regarding).
'charge for' becomes 'fee' (I've seen this in other clues).
'finishing order' becomes 'r' (I can't justify this - if you can you should give a lot more credence to this answer).
're'+'fee'+'r'='refeer'
'refeer' reversed gives 'REEFER'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for reefer that I've seen before include "Warm jacket - cannabis cigarette" , "Type of jacket - smoke" , "Kind of jacket - joint" , "Smoking jacket and cigarette" , "Hand-rolled cigarette" .)