The medi-kit combines a healing facility with pain killers and stimulants. In order to use the medi-kit you must face towards the soldier requiring treatment. If the soldier is stunned you must stand over the body. Click on the medi-kit icon and select 'use medi-kit' from the menu.
HEALING> Red body parts show fatal wounds. Click on a body part that is wounded. Click on the 'Heal' button. One fatal wound will be cured and some health restored.
STIMULANT> This will restore energy and revive unconscious (stunned) soldiers. In order to revive an unconscious soldier you must stand directly over the body.
PAIN KILLER> This will restore the morale of wounded soldiers up to an amount equivalent to the soldier's lost health.