Virtualhosts allow you to host multiple websites on a single webserver. Shared hosting is based on this idea as this allows multiple customers to use a single server. It does require some configuration.
The previous backup script is a bit limited as it always creates a full backup. Let' adjust that to create incremental backups.
Numerical permissions describe the permissions of the file or folders and is most likely known with FTP or the unix filesystem. This post explains the meaning of those numbers.
This easy backup script creates a .tar.gz for a certain folder. The script can be used to backup a full folder once or scheduled.