IIS is Microsofts implementation of a web server for Windows. It’s free to use with Windows Server and can even be deployed on a Windows 10 machine. IIS is an easy to use GUI and may be preferred over Apache or NGINX when building web apps that fully utilize the Microsoft Stack.
Virtual Hosts are used in Apache to allow a single web server to serve numerous websites. Basically www.FailedNormal.com point to /var/www/FailedNormal, and www.EliTheComputerGuy.com points to /var/www/EliTheComputerGuy.