Helpful creature shows way to get good marks (7,6)
I believe the answer is:
brownie points
'good marks' is the definition.
(I've seen this before)
'helpful creature shows' is the wordplay.
'helpful creature' becomes 'brownie' (I am not sure about this - if you are sure you should believe this answer much more).
'shows' becomes 'points' ('point' can be a synonym of 'show').
'brownie'+'points'='BROWNIE POINTS'
'way to get' is the link.
Can you help me to learn more?
(Other definitions for brownie points that I've seen before include "approbation" , "Notional awards for good work" , "Notional credit marks" , "Marks earned for doing right?" , "Credit for doing well" .)