He shows that to blunder is nothing for a learner (5)
I believe the answer is:
errol
'he' is the definition.
'that to blunder is nothing for a learner' is the wordplay.
'that to blunder' becomes 'err' (to err is to make a mistake or blunder).
'is nothing' becomes 'o' (looks like zero - 0).
'for' is a charade indicator (letters next to each other).
'a learner' becomes 'l' (as in a learner driver with L-plates on their car).
'err'+'o'+'l'='ERROL'
'shows' is the link.
(Other definitions for errol that I've seen before include "- Flynn, US film actor" , "- Flynn, twentieth century film actor" , "-- Flynn, Hollywood actor" , "Old film star" , "- - Flynn, film star" .)