Help to make a curtain, say (5)
I believe the answer is:
avail
'help' is the definition.
('avail' can be a synonym of 'help')
'a curtain say' is the wordplay.
'curtain' becomes 'veil' (I've seen this before).
'say' indicates a 'sounds like' (homophone) clue.
'veil' sounds like 'vail'.
'a'+'vail'='AVAIL'
'to make' acts as a link.
(Other definitions for avail that I've seen before include "Use to one's advantage" , "(Of no) use or benefit" , "Help, benefit" , "Provide help; profit" , "Be of value to" .)