Follow the step below to backup your iPhone using iCloud
1. First your iPhone must be connected to WiFi
2. Go to Setting> [Your ID] - your name and tap iCloud
3. Tap "Back Up Now". Ensure your Wi-Fi network is always on until the backup is completed.
4. Once it is finished go to check the file: Go to Settings> Your ID [Your name]> iCloud >iCloud Storage >Manage Storage, then select your device. The backup file should be appearing there.
iCloud Automatic Backup.
1. Make sure iCloud is turned on in Settings > Your ID (your name] > iCloud > iCloud Backup.
2. Connect to the charger
3. Connect to Wi-Fi
4. The device's screen must be locked
5. Check also if the storage is enough to hold the backup data. You can upgrade iCloud storage by purchasing it from the iPhone itself. Apple only provides 5GB free storage in iCloud
Backup iPhone from iTunes
1. Open iTune and select your device in the list
2. Go to Summary and click Backup Now