1. For example, if you want to connect computer C by computer A, where A is in country 1 and C is in country 3 and behind a router with no NAT is set. General method is creating a port forward on C side router. It is very clear and very simple if you are very good in IT. But if the router is not allowed you to setup (control by administrator), you cannot create port forward on router. Then you cannot connect by standard routing.
2. If both 2 computers can access Internet, they can be connected virtually under all kind of TCP/IP network. Even though you are not good in IT, you can connect easily.
3. If your office network/firewall is allowed only port 80 to connect out, then using Magic Router Forwarder Client will bypass firewall detection.
4. Access computer D by computer C, by easily setting up port forward definition on listener client.
5. See more on Sample Application forum, there are more clear description and diagrams.