Hi Don, I think you could be confusing things. DotNetNuke can host MANY portals within it, unlike a standard WordPress website which can only host one on a Linux server or Windows configured to run PHP apps. I can explain a couple of examples of what I think you may mean.
Scenario 1 - You have a top level domain with several sites that relate to it. You are able to put top level domain name on the main portal and configure many portals which are on the same code base by building child sites and pointing the correct domain records to it, which can be done by pointing the domain, adding to IIS and then when you build the 'child site' adding in that domain name and it will be become live immediately with a default template. So, www.domain.com and then childname.domain.com and then childname2.domain.com could all have their own stand alone websites, but share modules and content throughout, even share designs.
Scenario 2 - You are a small marketing agency and want to manage a few sites but don't want to have a big involvement in having lots of custom websites to handle - so this scenario allows you to do the same thing - create a parent portal and build many websites within that one codebase using the same techniques. You can also have staging urls, build the site and when the customer wants to go live, just add in the domain into IIS and the portal alias section of the website and you have a full website of it's own, looking completely different, on it's own url within one instance of DNN.
But, to my knowledge, you cannot host a WordPress website in a DotNetNuke website.
I hope this clarifies your thinking on this topic.