Complex sentence: It gives the rules for an army of Beastmen and monsters as a stand alone army; it can also be used as extra rules for a Hordes of Chaos army, or a mix of both.
Split into simpler sentences: It gives the rules for an army of Beastmen and monsters as and stand alone army. But it can be used as extra rules for an Hordes of Chaos army to, or a mix of both.