Just a couple of comments.
The line below doesn't backup the file to /home, it actually backs up both /www and /home to the tape drive. The stuff in /dev usually represent devices on the system. "st" means "Scsi Tape". The 0 means the first scsi tape.
tar -cvf /dev/st0 /www /home 2>/dev/null
The following line is, quite frankly, a mess. Why someone would write something convoluted like this, I'll never know.
[ $? -eq 0 ] && status="Success!" || status="Failed!!!"
Here it is, rewritten to be more clear.
if [ $returnCode -eq 0 ]
The line above invokes the mail system to send email to email@example.com
with subject line 'Backup status'.
Normally, the mail system will read the contents of the email from stdin (the keyboard). If you wanted to email he contents of a file (/tmp/mailbody.txt), you could have used this:
The "<<" is a special item called a "here document". It means, "I want you to redirect the input of this command from a file - Oh, and by the way, here is the content of the file."
The "END_OF_MAIL" is just a string that defines the start and end of the 'file' contents to be redirected into the command.
This is very useful as it obviates the need to create an intermediate file.