Automatically back up data on your iOS device like your photo library, settings, accounts and other information to your iCloud account in order to keep it secure and accessible for restoring your device with. iCloud will automatically back up when your device is plugged in, locked and connected to Wi-Fi. Turn this feature on by following the steps below.
Check out this video for more details:
Note: iCloud accounts have 5GB of free storage. Over time, this may fill up and not be enough to continue backing up your device. If this situation arises, consider upgrading your iCloud storage.