I actually figured this out by just clicking on everything could find when I first got the
app, but you feed your zombies by tapping the button in the bottom left corner that says
invade. Your can invade every two hours. When you invade, you need at least eight zombies.
What you do, is choose which farm you want to invade, and which order you want your
zombies to go in. Then, when the bar above the first zombie is full. It will have a
picture of a brain by it. Tap the brain, and hot zombie will attack the farmers. Then, do
the same for the rest of your zombies.

if you tap above their heads they will be ready to attack faster. the hungrier they are
the better. with little to no hunger they get distracted easily and you'll see them say no
and they will say it often, this can lead to losing numerous zombies in an attack.

the LESS zombies you lose the MORE gold you get for winning.

just battle