You need a static I.P address, Forward port 25565, to see if your port is open have the mincecraft server
RUNNING and then go to:
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If it is then Kudos to you. :y:
you'll also have to set up your mods Ect... so you can use server comands / build shit by adding your usernames to 'ops.txt' and 'whitelist.txt'
Once you've set up connect by either typing in your external I.P (your buddy will need this) into the multilayer menu on minecraft of type 'localhost'. If you really get stuck ill re-download team viewer.