Step 1: Copy URL of Youtube's video.
The URL must be HTTPS, if it's just HTTP without the S, it will NOT work, you can always add the S later on.
Step 2: In "Post a new topic" (aka edit mode) Click on the YOUTUBE button that you see in the upper menu. That will create the youtube codes.
Step 3: Insert the video URL between the YOUTUBE codes like so. Once again, if the URL is just HTTP, it won't work so add the "S" now if you didn't already. Also, do not add any empty spaces between the Youtube codes and the video URL.
Once you are done, you should see the video below your post like in this case here...
Cheers,
Merlin
https://www.youtube.com/watch?v=ftjEcrrf7r0[/youtube]