It shows where to put something in the car, etc. (5)
I believe the answer is:
caret
'it shows where to put something in' is the definition.
The definition suggests a singular noun which matches the answer.
'car etc' is the wordplay.
'etc' becomes 'et' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'car'+'et'='CARET'
'the' is the link.
Can you help me to learn more?
(Other definitions for caret that I've seen before include "Indicator of omission" , "Proofreading sign for 'Insert'" , "Weeding tool" , "It shows what to put in" , "Proofreader's sign of omission" .)