Curious about DNS settings and Joomla

Will Joomla know where to send people once they get to the IP that Joomla is on? Are settings needed to be set in Apache also? I assume DNS settings need to point at the same IP as the Main Joomla server.

Please inform.
thank you

I found that "it just worked" for my site. The documentation for the hosting package said that

So iphone.yourdomain.com just worked. If you try it and it's not working, and you are your hosting company, then the article on
content.websitegear.com/article/subdomain_setup.htm
may be of help.