I have always wondered about this. Why do people always suggest hamachi/evolve? What happened to entering IP addresses and opening a port in your router? That is the way I used to play multiplayer games with my friends. Different generation I guess..
Here is a tutorial on how use LAN mode with your friend. What you will need:
-Look up your IP address
-Configure your router for port forwarding
If you have never heard of these terms then I recommend using hamachi instead.
There is a host and a client. The host starts the game and the clients join that game.
Instructions for the host-Go to your router settings, allow port 7911 (port forwarding)
http://www.whatsmyip.org/ -Give that IP address to your friend.
-Open ygopro. Select Multiplayer -> LAN Mode -> Host -> OK
Instructions for the client:-Open ygopro. Select Multiplayer -> LAN Mode
-In HostIP enter the host IP address. In the field next to that enter 7911.
-Click Join