You can restore content from an iCloud backup when, for instance, you update the phone software. To restore the content, you need to back up the phone memory to iCloud.
You can restore content from an iCloud backup when your phone is activated for the first time and after a factory reset. When this screen is displayed, your phone is ready to restore content from an iCloud backup.
Press Restore from iCloud Backup.
Press the field next to "Apple ID" and key in the username for your Apple ID.
Press the field next to "Password" and key in the password for your Apple ID.
Press the required backup and your phone restores the content of the selected backup. Subsequently, follow the instructions on the screen to set up your phone and prepare it for use.