There are two parts to this. The first one is that you must issue a directive which gives Apache an IP address to serve the name based domains from. Like this:
PHP Code:
# If you want to use name-based virtual hosts you need to define at
# least one IP address (and port number) for them.
#
NameVirtualHost 12.34.56.78:80
The second part is then to add the VirtualHost directives for each domain. Like this:
PHP Code:
# VirtualHost example (name based):
# Almost any Apache directive may go into a VirtualHost container.
#
<VirtualHost name.of.host.some_domain.com/>
ServerAdmin webmaster@host.some_domain.com
DocumentRoot /www/docs/host.some_domain.com
ServerName host.some_domain.com/
ErrorLog logs/host.some_domain.com-error_log
CustomLog logs/host.some_domain.com-access_log common
</VirtualHost>
This is just a basic outline there are many differnet ways to write your virtual host within your httpd file.