This article describes how can you autoplay youtube videos that you have embedded or want to embed into your website. The trick is simple. I hope you know the steps of how to embed a youtube video.
First go to www.youtube.com and find the relevant video.
When you open the video, click on share and then click embed.
Now here is the code that I got. Would be a little different for you,
Now after <iframe width="420" height="315" src="http://www.youtube.com/embed/pFsRBFrFM9Q add ?fs=1&hl=en_GB&rel=0&autoplay=1 and then add "frameborder="0" allowfullscreen></iframe>
So basically you have to add ?fs=1&hl=en_GB&rel=0&autoplay=1 in between of your code like I told you. Hope that helps. Thanks