It depends where your friend is. If he or she is in the same house as you then you need Direct Connect URL for WoM
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Same House:To get one, simply follow this template:
mc://<LocalIP:Port><UsernameConnectingToServer><ngi98hg0inofndTo find local Ip, go on the computer hosting the server
-> Start -> Run -> Cmd
At Cmd type "ipconfig" find where it says "IPv4 Address:"
Use the "IPv4 Address in "LocalIp" above.
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If your friend is in a different area than you then you may have to Port Forward.To port forward, goto
http://portforward.com/ and choose your router name and model number (usually on the bottom)
Once the info is entered, if will give you step by step instructions on how to Port Forward
Hope this helped.