Inserting a video

I have completely forgotten how to insert a video. I copied the link, clicked on HTML and tried to paste in this:

[ Moderator note: Please use the code button or backtick for code and not the single quote. ]

http://erniealmond.com

<iframe width="420" height="315" src="http://www.youtube.com/embed/tH_cXjCqmCk?rel=0" frameborder="0" allowfullscreen></iframe>

But I obviousley missed something! I can’t find any instructions on the help forum.