Well, here it is. Tried to make it as Newb friendly as possible.
Open the directory named "World of Warcraft"* and in there you should find a file named "realmlist.wtf". Double-click** on the file*** and then choose to open it with a program named "Notebook"****. Now, edit it so it looks like this:
set realmlist <what the server is named, in this case i use my own little private server (not public): 127.0.0.1>
just delete the set patchlist, you dont need it...
* If you renamed it you are really stupid.
**Click two times with the left mouse button on it.
***Realmlist.wtf
****If you deleted it, you are even more stupid than *