In terms of what? A web browser sends along the hostname you typed in your browser bar when it connects to the web server, so it knows what site to direct the user to (if you have name based virtual hosting turned on). You can use cname's combined with name based virtual hosting to host multiple sites on the same ip address (no ssl though).
how to configure CNAME record? and how if i use name server from my web hosting company not use name server from domain register? Should i set up at web hosting?