A medal and disc used by soldiers (4)
I believe the answer is:
ammo
'a medal and disc used by soldiers' is the definition.
I can't tell whether this definition defines the answer.
'a medal and disc' is the wordplay.
'medal' becomes 'MM' (Military Medal).
'and' says to put letters next to each other.
'disc' becomes 'O' (disc-shaped letter).
'a'+'mm'+'o'='AMMO'
Can you help me to learn more?
(Other definitions for ammo that I've seen before include "essential supplies for soldiers" , "Contents of magazine" , "arms" , "Bullets and bombs, etc (abbr)" , "Bullet" .)