You put in the youtube tags which are [_youtube_] and [_/youtube_] without the '_'. Which if you got advanced view you can just hit the youtube button and it will populate the tags for you
In between those you get the ID of the youtube video which is typically found in the URL....
for example the one in your post is IVGeReOaU
So your complete line would look like:
[_YOUTUBE_]xIVGeReOaU[_/YOUTUBE_] again without the '_'
Apparently however, the video you mentioned does not exist which is one reason why the link is only showing up and the embedding is not working. the video has to be a valid video