Quoting from man bash
:
-c string If the -c option is present, then commands are read
from string.
If there are arguments after the string, they are assigned to the positional parameters, starting with $0.
The command quoted by you would append the text in heredoc (i.e. the text in VirtualHost
tag) to the file /etc/apache2/sites-available/magento-store.com
.