Biro twist makes star shape (9)
I believe the answer is:
pentangle
'star shape' is the definition.
'pentangle' can be an answer for 'star' (I've seen this before). I'm not sure about the 'shape' bit.
'biro twist' is the wordplay.
'biro' becomes 'pen' (I can't justify this - if you can you should give a lot more credence to this answer).
'twist' becomes 'tangle' (tangling is a kind of twisting).
'pen'+'tangle'='PENTANGLE'
'makes' is the link.
Can you help me to learn more?
(Other definitions for pentangle that I've seen before include "Five-pointed star" , "Pentagram" , "mystic symbol" .)