The easiest way to backup your website is by doing so via CPanel.
By logging into CPanel, you will have an Icon that says Backup. Once you start the backup, it runs in the background and will email you when it's ready and you can FTP in and grab the backup.
Note: We strongly encourage you to backup your site on your own servers and not rely on our backup methods. You can also restore a backup via CPanel as well.
For more information, please visit our video tutorial at http://www.cpanel.net/media/tutorials/backup.htm