It's used by entrants to put the screen back (4)
I believe the answer is:
door
'it's used by entrants to put' is the definition.
I can't judge whether this defines the answer.
'screen back' is the wordplay.
'screen' becomes 'rood screen' (rood screen is a kind of screen).
'back' is a reversal indicator.
'rood' in reverse letter order is 'DOOR'.
'the' is the link.
Can you help me to learn more?
(Other definitions for door that I've seen before include "Threshold" , "Entrance way" , "Barrier to open and close" , "Swinging barrier" , "Jim Morrison?" .)