When posting or replying you will notice a new YouTube icon in the editor window.
This icon will insert all the code you need.
Simply enter the YouTube video ID which can be found in the URL of the video you are watching:
Code:
http://youtube.com/watch?v=JFwCCL0Vh6U
Then enter this between the [ YOUTUBE ] tags:
HTML:
[MEDIA=youtube]JFwCCL0Vh6U[/MEDIA]
Which will result in the video displaying: