As you can tell from the explainer video, you're not taking on your opponents directly, Instead, when you choose another player to compete against, you'll set up plants in your backyard, then launch a massive wave of zombies. You'll gather points from the number of zombies that you kill as well as how far back on the playing field you kill them. You can watch the score comparison change in a new banner set at the top of the Battlez stage. When the battle is over, you can see which plants your enemy used, which might give you some hints as to which plants to use in future battles. You'll also get a progressively better reward the more games you win in a row.