I want to know more about the Plesk Backup.

The Plesk backup is a backup facility built into your Hosting control panel that will create a snapshot of your entire account.  Should anything go wrong, you will be able to use that backup to restore your account to the backup version.  This includes web space, databases, email accounts and all your settings.  You will have the option, once you have created this backup, to save a copy to your hard drive.  You can also create the backup in a separate web space provided you have the correct FTP details.