You first grab the link
http://www.youtube.com/watch?v=BytKSy8M4bk
Notice that
BytKSy8M4bk
Put that between [ youtube]BytKSy8M4bk[ /youtube] and you are set to go
If you would like more please visit the vast selection devoted to "New BBcode [youtube] [googlevideo] [metacafe] [revver]" in the library.