You mean here on AHS?
You just take the code from the URL, of the youtube video you want to embed.
For example:
Let's take this URL
http://www.youtube.com/watch?v=Zz2Fgdbj9lc
What you want is the code at the end:
Zz2Fgdbj9lc
And so, all you need is to write it like this:
Code:
[.youtube]Zz2Fgdbj9lc[./youtube]
(without the dots).
And you will get the result:
Hope this helped