If you have a Windows-based server, you probably want to expose it to the internet to do things like host websites. To do that, you have to install Microsoft's web server, Internet Information Services (more commonly known as IIS).
You can click a role for a description of it or get more information from Microsoft.
Your server will now go through the process of installing IIS, which can take a while. Once it's done, you'll receive a flag in the Server Manager.