Here's the lowdown: By using portals you can run multiple websites with unique domains on a single installation of DotNetNuke.
A popular feature of DotNetNuke is the ability to create multiple parent and child portals. DotNetNuke portals allow you to create multiple websites—with unique domain names—using one installation of DotNetNuke.
You need an active installation of DotNetNuke on a Deluxe or Premium Windows shared hosting account to setup multiple portals with multiple domains.
You need an available template to create a new portal. Click Export Template to export an existing template for the new portal.
When complete, your new portal will display when you browse to the secondary domain.
If your Website does not resolve, note that it can take 24 to 48 hours for other networks to recognize the secondary domain. If you see the default portal, verify that you specified the correct folder in the Portal Alias field.