Beginner admitting learner is to have difficulties (8)
I believe the answer is:
flounder
'to have difficulties' is the definition.
(to flounder is to be in difficulty)
'beginner admitting learner' is the wordplay.
'beginner' becomes 'founder' (someone who founded something).
'admitting' indicates putting letters inside (admit can mean to welcome in or accept).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'founder' going around 'l' is 'FLOUNDER'.
'is' acts as a link.
(Other definitions for flounder that I've seen before include "Fish -- stumble helplessly" , "Have difficulties with the flatfish" , "Predatory fish" , "Be out of one's depth" , "Move clumsily like flatfish?" .)