Real Networking Interfaces are the actual physical network connections on a computer. For example, an Ethernet wire or wireless card is a real networking interface.
If an interface is only a tunnel through another interface, then it is a Guide to Unix/Explanations/Fake Networking Interface.
Normally, there is somewhere in the Boot Process that configures network connections. Use the ifconfig command as root, though some Unix variants have a different command. A common configuration is to do DHCP with dhclient or pump command.
It is also possible to route packets between interfaces. This requires configuring the interfaces correctly and making a routing table. A firewall is a good idea.