Army student acted strangely (5)
I believe the answer is:
cadet
'army student' is the definition.
'cadet' can be an answer for 'student' (I have seen 'Military student ' mean 'cadet' so perhaps 'student' could also mean 'cadet'). I am unsure of the 'army' bit.
'acted strangely' is the wordplay.
'strangely' indicates an anagram.
'acted' is an anagram of 'CADET'.
Can you help me to learn more?
(Other definitions for cadet that I've seen before include "Junior officer; younger brother" , "Younger son" , "Officer in training" , "recruit" , "A trainee army officer" .)