So I'm playing wow again.
The last time I played (a year or so ago or so) I added a few peoples as my Real ID Friends. Now that I'm back I'm clicking around the wow GUI and I can't figure out how to send them a message.
I haven't played WoW for a few months, but your RealID Friends should show up at the top of your friends list when you open the Social panel, on the friends tab.
You can start by opening your friends list, they should show up there. You can right click them to send a message.
There is also an icon on the top right of the chat window what will show your friends list.