1. Connect your external hard drive. 2. Open Settings: Press Windows key + I. 3. Go to System > Storage > Advanced storage settings > Backup ...
Select Start > Settings > Update & Security > Backup > Add a Drive, and then choose an external drive or network location for your backups.
Easy done with using the built-in windows facilities. Control Panel -> Backup and restore (Windows 7) -> System Image Backup. -> backup to you external HDD.