Step 1 Add your friends on the forum by following them
Step 2 go into waw and go into private match then open console with ~ then type xpartygo (it will automatically throw you in a private match of your own)
Step 3 tell your friend to press F10 and double click on your name in the friends list tab
Step 4 your in the game with your friend and hope you have fun!
hope this helps since I recently figure this out if any questions I'll try to answer them as best as I can
You all have a lovely day 