VPNs, or Virtual Private Networks, allow people to connect to one another as if they were within the same local network. Using VPNs helps add a layer of anonymity and prevents people from needing to know your actual IP address. There are dozens, even hundreds of VPN applications available, but by and large, /tg/ uses Hamachi.
Find it here: LogMeIn: Hamachi.cc
As noted above, Hamachi is the VPN tool of choice for /tg/, allowing players to anonymously connect to a virtual network for gaming with Virtual Tabletops. Hamachi is free, easy to install and configure, and extremely simple to operate. I will eventually put a step-by-step guide here, but it's pretty straightfoward.