A simple Azure ARM template illustrating use of the uniqueName function.

simple_vm_arm.json

{
    "$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
    "contentVersion": "1.0.0.0",
    "parameters": {
        "location": {
            "type": "string",
            "defaultValue": "centralus"
        },
        "virtualMachineSize": {
            "type": "string",
            "defaultValue": "Standard_A1_v2"
        },
        "adminUsername": {
            "type": "string"
        },
        "adminPassword": {
            "type": "securestring"
        },
        "virtualNetworkResourceGroupName": {
            "type": "string"
        },
        "virtualNetworkName": {
            "type": "string"
        },
        "subnetName": {
            "type": "string",
            "defaultValue": "Subnet"
        },
        "networkSecurityGroupName": {
            "type": "string"
        }
    },
    "variables": {
        "vnetId": "[resourceId(parameters('virtualNetworkResourceGroupName'),'Microsoft.Network/virtualNetworks', parameters('virtualNetworkName'))]",
        "subnetRef": "[concat(variables('vnetId'), '/subnets/', parameters('subnetName'))]",
        "virtualMachineName": "[concat('vm', uniqueString(resourceGroup().id, deployment().name))]",
        "networkInterfaceName": "[concat(variables('virtualMachineName'), '_nic')]",
        "numberOfDataDisks": 2,
        "sizeOfDataDisksInGb": 31,
        "diskCaching": "ReadWrite"
    },
    "resources": [
        {
            "name": "[variables('virtualMachineName')]",
            "type": "Microsoft.Compute/virtualMachines",
            "apiVersion": "2016-04-30-preview",
            "location": "[parameters('location')]",
            "dependsOn": [
                "[concat('Microsoft.Network/networkInterfaces/', variables('networkInterfaceName'))]"
            ],
            "properties": {
                "osProfile": {
                    "computerName": "[variables('virtualMachineName')]",
                    "adminUsername": "[parameters('adminUsername')]",
                    "adminPassword": "[parameters('adminPassword')]"
                },
                "hardwareProfile": {
                    "vmSize": "[parameters('virtualMachineSize')]"
                },
                "storageProfile": {
                    "imageReference": {
                        "publisher": "Canonical",
                        "offer": "UbuntuServer",
                        "sku": "16.04-LTS",
                        "version": "latest"
                    },
                    "osDisk": {
                        "createOption": "fromImage",
                        "managedDisk": {
                            "storageAccountType": "Standard_LRS"
                        }
                    },
                    "copy": [
                        {
                            "name": "dataDisks",
                            "count": "[variables('numberOfDataDisks')]",
                            "input": {
                                "caching": "[variables('diskCaching')]",
                                "diskSizeGB": "[variables('sizeOfDataDisksInGb')]",
                                "lun": "[copyIndex('dataDisks')]",
                                "name": "[concat(variables('virtualMachineName'), '-datadisk', copyIndex('dataDisks'))]",                                
                                "createOption": "Empty",
                                "managedDisk": {
                                    "storageAccountType": "Standard_LRS"                                  
                                }
                            }
                        }
                    ]
                },
                "networkProfile": {
                    "networkInterfaces": [
                        {
                            "id": "[resourceId('Microsoft.Network/networkInterfaces', variables('networkInterfaceName'))]"
                        }
                    ]
                }
            }
        },
        {
            "name": "[variables('networkInterfaceName')]",
            "type": "Microsoft.Network/networkInterfaces",
            "apiVersion": "2016-09-01",
            "location": "[parameters('location')]",
            "dependsOn": [
                "[concat('Microsoft.Network/networkSecurityGroups/', parameters('networkSecurityGroupName'))]"
            ],
            "properties": {
                "ipConfigurations": [
                    {
                        "name": "ipconfig1",
                        "properties": {
                            "subnet": {
                                "id": "[variables('subnetRef')]"
                            },
                            "privateIPAllocationMethod": "Dynamic"
                        }
                    }
                ],
                "networkSecurityGroup": {
                    "id": "[resourceId('Microsoft.Network/networkSecurityGroups', parameters('networkSecurityGroupName'))]"
                }
            }
        },
        {
            "name": "[parameters('networkSecurityGroupName')]",
            "type": "Microsoft.Network/networkSecurityGroups",
            "apiVersion": "2017-06-01",
            "location": "[parameters('location')]",
            "properties": {
                "securityRules": [
                    {
                        "name": "default-allow-ssh",
                        "properties": {
                            "priority": 1000,
                            "protocol": "TCP",
                            "access": "Allow",
                            "direction": "Inbound",
                            "sourceAddressPrefix": "*",
                            "sourcePortRange": "*",
                            "destinationAddressPrefix": "*",
                            "destinationPortRange": "22"
                        }
                    }
                ]
            }
        }
    ],
    "outputs": {
        "adminUsername": {
            "type": "string",
            "value": "[parameters('adminUsername')]"
        }
    }
}