Turn helping to secure book collection (8)
I believe the answer is:
rotation
'turn' is the definition.
(rotation is a kind of turn)
'helping to secure book collection' is the wordplay.
'helping' becomes 'ration' (a ration is a serving or helping).
'to secure' means one lot of letters goes inside another (inserted letters are secured inside).
'book collection' becomes 'ot' (I can't explain this - if you can you should believe this answer much more).
'ration' placed around 'ot' is 'ROTATION'.
Can you help me to learn more?
(Other definitions for rotation that I've seen before include "The action of moving around an orbit" , "Cycle - revolution" , "Going round" , "Turn of a wheel" , "Recurrent order" .)