Once the Function App is created, you will see that the sample has used MS Deploy extension and set the packageUri parameter and you assign the value to your function app zip (deployed in a storage account or access over the internet). Once the function app resource is created the below ARM template will deploy the function app code on your depended resource.
{
"apiVersion": "2014-06-01",
"name": "MSDeploy",
"type": "Extensions",
"dependsOn": [
"[concat('Microsoft.Web/Sites/', parameters('name'))]",
],
"properties": {
"packageUri": "https://auxmktplceprod.blob.core.windows.net/packages/wordpress-4.2.4-IIS.zip",
}