Two of the Germans are kids and two are old men. They're all wearing hand-me-downs from dead soldiers.
The fifth is their commander, a tough old soldier who has been wounded four times and then sent back to war.
The commander's boots are pretty much the only thing he owns; he believes that if you look deeply enough into the polish on them, you can see Adam and Eve.
Billy looks deep into the German commander's boots and sees Adam and Eve.