Send the French up in stages for folded flaps on their coats (6)
I believe the answer is:
lapels
'stages for folded flaps on their coats' is the definition.
I can't judge whether this definition defines the answer.
'send the french up in' is the wordplay.
'send' becomes 'laps' (I can't justify this - if you can you should believe this answer much more).
'the french' becomes 'le' ('the' in French).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'in' means one lot of letters goes inside another.
'le' back-to-front is 'el'.
'laps' enclosing 'el' is 'LAPELS'.
Can you help me to learn more?
(Other definitions for lapels that I've seen before include "Parts of collars" , "flower wearers?" , "Folded-back flaps on front of coat" , "They turn back on the front" , "Folded flaps at front of coat" .)