The parameters for the appserviceplan-1.0.0.0 ARM template are as follows:

  "parameters": {
    "customTags": { "type": "object" },
    "appServicePlanName": { "type": "string" },
    "appServicePlanSkuTier": { "type": "string" },
    "appServicePlanSkuName": { "type": "string" }
  },

And the resources for this template include a single resource of type Microsoft.Web/serverfarms. This resource is responsible for creating an App Service plan. The code for this resource is listed next:

    {
      "type": "Microsoft.Web/serverfarms",
      "kind": "app",
      "name": "[parameters('appServicePlanName')]",
      "location": "[resourceGroup().location]",
      "apiVersion": "2016-09-01",
      "tags": "[parameters('customTags')]",
      "properties": {
        "name": "[parameters('appServicePlanName')]"
      },
      "sku": {
        "Tier": "[parameters('appServicePlanSkuTier')]",
        "Name": "[parameters('appServicePlanSkuName')]"
      }
    }

Notice how all the important properties are provided values from parameters. This makes this template generic and reusable.