As it is stated on VirtNet page it is just dummy network interface which does not do anything special itself (similar to MS loopback adapter, but supports all Windows operating systems). However, when used in combination with WinpkFilter you can build various virtual network environments over it.
WinpkFilter can be used for implementing two major tasks:
1) To indicate packets from the name of VirtNet to TCP/IP stack.
2) To intercept packets sent by TCP/IP stack to VirtNet network interface.
You can create pure virtual network environment or bridge it to the real network or …. Actually, it depends only from you requirements.