overcoming flood

Congratulations on getting that far in the game. The first thing you need to do is kill some of the first 'zombies' in order to get a shotgun(which every time I've played I've found one), and then use it along with a battle rifle and plenty of grenades to annihilate the zombies. It's pretty much just killing large waves of enemies without any real tactical moves necessary

My husband is a gamer, and one of his favorite games is halo so all I can say is that you really need to keep just shooting, and they'll eventually all die... so just keep on shooting.