Its easy

1. go to youtube
2. find the video you want to embed
3. do NOT press the button for embeding videos from youtube but JUST copy the URL (adress in the browser)

have a brake

4. click here on the youtube button at the top of this message window
wich will create this [ embed ][ /embed ]
5. then post the url just inbetween these codes like
[ embed ]http://www.youtube URL 0f your video HERE[ /embed ]
and your video should apear after ....
6. ... you press the submit button at the buttom of this message window