Code help

Can anyone kinda break this script down for me and explain what it does?


_root.bullet_a = new Array(300);
for (var bulletnull = 0; bulletnull<300; bulletnull++) {
_root.bullet_a[bulletnull] = 0;
}
_root.debris_a = new Array(600);
for (var debrisnull = 0; debrisnull<600; debrisnull++) {
_root.debris_a[debrisnull] = 0;
}