The GUI is divided into three section
The bottom panel of Soldiers in Hand, each one with Health, XP and Ammo bars. Also, there's a medal bar depicting the veteran status and access to advanced weaponery.
The right popup panel is the Ammo Dump, from it you can arm your soldier, resupply his ammo and rejuvinate his health. Soldiers on field can't be resupplied, they need to return to base by 'regroup'ing.
The left popup is the soldier specific panel, where you can check and load your soldier with weapons, ammo and rejuvinate his health. Also, this panel is used for upgrading the soldier veteran status following 3 career paths. Soldier can only be equipped with weapons matching his veteran status. Once a soldier gains full xp on his current weapon, you can upgrade his veteran status and access advanced weaponery.