You can see what is currently setup in the sites-enabled directory (etc/apache2/sites-enabled IIRC) then create a new site in the sites-available dir (/etc/apache2/sites-available IIRC) - I'd recommend copying one that's there already and use that as a template. Then enable your site (there's a command you'll find if you google, although AFAIK simply creating a symlink will have the same effect).

All this can be done with Webmin too, which is probably easier if you're not familiar with Apache