You can create multiple distinct, (mainly) independent websites with one instance of a DNN installation on your web account. In lamens terms, this means that you can purchase ONE web hosting account with ONE database and ONE DNN Install and be able to set up www.MyFirstWebsite.com, www.MySecondWebsite.com, www.MyUnrelatedOtherWebsite.com, etc and DNN will power them all as if they were completely different websites.
There are many advantages to this DNN Functionality; especially as it relates to total cost of ownership, staff training, cost and efficiency. Bottom Line: It makes dollars and cents!
However, that's not to say that other considerations should be overlooked. Don't forget, all of your websites would have to share the resources or rather, limitations on resources (ONE provider account, ONE server, etc) provided by your web hosting provider.
What this means is that if your web hosting account provides you with 1000 MB of HDD space and 100 MB RAM, it must be divvied up among the websites. This would also be a pretty good time to remind you that a default DNN Installation can consume 80-90 MB RAM straight out of the box. When you start adding features and modules, you may find that it is something for to consider. Think about how your websites will be used and the requirements they may have in order to plan accordingly. (These are also good things to keep in mind when shopping for a web host)
Now, to create a "second" website, you will need to do some set up in the DNN portal. *YOU MUST BE LOGGED IN AS THE HOST TO SETUP A SECONDARY WEBSITE* It's a fairly quick and straightforward process using the built in DNN interface. You will have to first decide if you will create a "Child Portal" or a "ParentPortal". Essentially, these two concepts are nearly identical and really only differ in two ways. First, they differentiate in the way DNN will render, or create, the website url. Second, they are different in terms of storage within the root www folder.
For example, the parent portal, "www.MySecondWebsite.com" will have a "root" folder created here: \wwwroot\Portals\PortalID\ (where PortalID is actually a number like "1" or "9" or other number. Parent Portals are issued a "PortalID" in subsequent order as they are created). Alternatively, with a "ChildPortal", the "root folder" is created as a sub-directory of the wwwroot\ChildPortalName\ and the URL is built as such: www.MyFirstWebsite.com/myChildWebsite .
Now, with one codebase and one database you can implement numerous websites, all of which get to access and utilize the common resources such as modules and global settings, and each of which also maintain a distinct user base and complete set of admin tools and settings; and all of which, can be globally administered with one login and completely customized and managed.
From the host login, for example, you can turn on & off the modules that a particular website (portal) gets to utilize, how many users a website can have, how much disk space to allocate, and even allow a maximum number of pages.
Making the possible scenarios even sweeter, you can enter PayPal information, charge the website owner (administrator) a monthly fee or even set an expiration date on any given website. Potential revenue out of the box.
Then, topping it all off with a cherry. . .it's DotNetNuke, its OpenSource and its Free. Want to use Authorize.net instead of PayPal? Grab the codebase and extend the application to meet your needs. Or, better yet, hire Virtual-Essentials.com to develop for you.
VIDEO: Setting Up Multiple Domain Names on Your Hosting Provider