What is a Virtual Server? Is that a website/domain that is provisioned for hosting? In IIS this is a website. What do you use to set this up…Webmin or Virtualmin?
Correct. A virtual server in Virtualmin is made up of a system and Webmin user account, a VirtualHost in Apache, a virtual domain in Postfix, a zone in BIND, and one or more databases in MySQL and/or PostgreSQL (confused yet?). When you create a virtual server, you’re creating a set of configuration options in all of these services that provides a connected set of capabilities to your customer or user. It is a “website” plus all of the stuff that is needed to make it useful for the full “I have a website” experience…mail, DNS, databases, directories for code and HTML, etc.
Webmin is the basis on which Virtualmin is built. It is a general purpose web-based UI for Linux and UNIX systems management. It is not intended to make virtual hosting “easy” or automatic. Virtualmin, which is a term that covers a bunch of Webmin modules and a custom theme, is the tool you want for managing virtual hosting accounts. If you want “websites”, you want Virtualmin (running on top of Webmin). If you just want to be a system administrator that doesn’t deal with virtual hosting, you want Webmin. Sounds like you definitely want Virtualmin, and Webmin by itself would just confuse you and make your life difficult.
What is the login to CPanel equivalent for Virtualmin login is that Usermin or VirtualMin? or Webmin?
Usermin is a webmail client. It is not in any way equivalent to anything cPanel does (though it does happen to have database management and a few other nifty features beyond being a mere webmail client). When you login to Virtualmin, you are logging into Webmin. Virtualmin is a module of Webmin.
So the equivalent to both cPanel and WHM is logging into Virtualmin. If your user is a virtual server account user, it’ll provide the same sorts of capabilities as cPanel. If your user is an administrative level user (root), you will have the full power of Virtualmin and Webmin (which is roughly comparable to WHM, though Virtualmin/Webmin has a lot more capabilities; Webmin alone has 113 standard modules for administering nearly every aspect of a Linux or UNIX system).
Is Webmin strictly for the root user of the server?
No. Webmin is the platform on which everything Virtualmin-related is built. Virtual server account holders login to Webmin to perform any administrative tasks (like creating mailboxes, editing databases, etc.).
1. Login Webmin 2. Create plan or Virtual server (not sure) 3. Create usersWe can’t tell you whether you want to create a plan or a virtual server! Which one do you want? 
A plan is what it sounds like, and pretty much the same as on cPanel. You set limits in a plan, and those limits can the be easily applied to new or existing virtual servers.
A virtual server is an account (a “website” with all the accoutrement).
For choosing which features are available, you’d probably start in the Features and Plugins page. From there, you might go to Server Templates, to get more specific. These don’t really have equivalents on cPanel…Virtualmin is quite a bit more flexible in these areas. With Server Templates, you could have one template that allows only web and MySQL, and another that allows web, mail, MySQL, BIND, etc. But if you know you only want web and MySQL, you should just disable the stuff you don’t want in Features and Plugins.