It's really quite simple.
(In server manager) first create an ibay (under 'Collaboration->Information bays') then create a new virtual domain (under 'Configuration->Domains') and point it to the ibay (the description field will be the denominator).
Then you can browse the domain from the formula
http://mydomain.xxx/virtualdomain or, if you created it as an extension to your primary domain from the formula
http://virtualdomain.yourdomain.xxxBut read the manual. It will tell you so much more !
Btw. Remember to load its 'html-folder' with htm-documents, one of which must be 'default.htm' or 'index.htm' (just so you have something to browse)!