in a nutshell...............boxer primed ammo has 1 hole, the hole is drilled center in the primer pocket of the brass.........no matter which way you rotate the brass, the primer hole is centered.......thus you can deprime the fired brass with a sizer die that has the depriming pin straight down the center.
berdan ammo has 2 holes but they are off center........somewhat more difficult to deprime since the center punch will miss those holes. that's why reloaders love the boxer primed ammo.....you can reuse the brass.
American commercial ammo is boxer primed, mil-surplus ammo is all berdan primed, there are certain exception, like RADWAY brit ammo, austian ammo, and a few others.......but on the whole they are all berdan primed.