1. First you need a server to play at. If you dont got anyone, find one here.
2. After you found one you'll need to search at the website for the realmlist witch always have "Set realmlist" infront.
3. After you found it go to your WoW folder witch usely is located at the C disc.
4. After entered it find Realmlist.wtf
5. Rightclick at it, and press OPEN IN NOTEPAD
If it doesn't shows. Doubleclick at realmlist.wtf. Check the text witch says: Open in another program. And a list will show up, open in NOTEPAD
6. Paste the realmlist (Set realmlist SOMETHING)
It looks complicated.. but it's very easy.