Networking for 1v1 rooms

I've been relentlessly trying to make sense out of the Networking system, but no matter what I just can't do it. I want to make a classic host-client connection, where a player becomes the host (server) with his own IP and a port, and the other player connects on that player's (server) IP address and port (he manually inserts the values).

What I tried was to start the server as localhost on the hosting player, and get his IP address with NetworkManager.singleton.networkAddress, but it doesn't seem to work or perhaps I missed something. Can someone open my mind in regard to this situation?