The plot? Yeah, some insane al-Qaeda radicals hijacked 4 American planes to crash into several different important US places. 2 went to the Twin Towers, 1 went into the Pentagon,and another got taken down into an empty field before it reached its target por the courageous passengers. They hated America, because we're awesome.
PS: I didn't see this was for school. I'm still gonna keep my answer but maybe tu should read the link. They can give tu way más information than any single person on fanpop can.