Store army leader learns about (7)
I believe the answer is:
arsenal
'store' is the definition.
(both can mean a stock or repository of something)
'army leader learns about' is the wordplay.
'leader' indicates taking the first letters.
'about' is an anagram indicator.
The initial letter of 'army' is 'a'.
'learns' is an anagram of 'rsenal'.
'a'+'rsenal'='ARSENAL'
(Other definitions for arsenal that I've seen before include "Store of weaponry" , "London premiership football team" , "English football club and military depot" , "Ammunition store or English soccer team" , "Military structure for arms and ammunitions" .)