Hello Michael,
its very easy, normally in a webtool you use:
<iframe width="854" height="510" src="//www.youtube.com/embed/60P7717-XOQ" frameborder="0" allowfullscreen></iframe>
to do this in a webnotebook use EmbeddedHTML[]. Note: you must change the "-signs by '- signs !
EmbeddedHTML[ "<iframe width='854' height='510' src='//www.youtube.com/embed/60P7717-XOQ' frameborder='0' allowfullscreen></iframe>"]
Just to be sure. Don't use this command in a Desktop notebook because it does not work and it provides no error.