Create the Website under IIS as shown below on port 80 so it can be accessed using http and give the appropriate hostname as required. The hostname should be available in the DNS records to access over Internet/Intranet.
Create the virtual directory as shown below. Use the default Pass-through authentication for demo purpose. You can also use Physical Path credentials on your folder if required and manage using Connect as button.
The below image shows how the Virtual Directory will look like under your website in IIS. So if you have a file saved under the Attachments folder under C:\Data\Attachments\doc1.docx, the URL to access the document will be http://mywebsite/attachments/doc1.docx. The folder can also be created on another physical drive on the same Server or can also be accessed using a UNC path.