Part of breathing apparatus is torn foolishly by learner (7)
I believe the answer is:
nostril
'part of breathing apparatus' is the definition.
'nostril' can be an answer for 'part' (nostril is a kind of part). I am not sure about the 'of breathing apparatus' bit.
'is torn foolishly by learner' is the wordplay.
'foolishly' indicates an anagram.
'by' is a charade indicator (letters next to each other).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'is'+'torn'='istorn'
'istorn' with letters rearranged gives 'nostri'.
'nostri'+'l'='NOSTRIL'
Can you help me to learn more?
(Other definitions for nostril that I've seen before include "Part of nose" , "A hole in the head" , "One of two holes in the head!" , "Through which one would snort" , "Nasal aperture" .)