To show a video from your website, first upload the video in YouTube.
After uploading the vidio add the following code in your website.
<object style="width: 360; height: 250; margin-top: auto; margin-bottom: auto; vertical-align: middle;">
<param name="movie" value="http://www.youtube.com/v/r-gDDUcaVqI&hl=en&fs=1>
</param>
<param name="allowFullScreen" value="true"> </param>
<embed src="http://www.youtube.com/v/r-gDDUcaVqI&hl=en&fs=1 type="application/x-shockwave-flash" allowfullscreen="true" width="360" height="250">
</embed>
</object>
In the param tag the value attribute holds the url of your video.
To change the display screen size simply change the width and height attribute
of the embed tag.
This is very simplet just copy and paste the code in your site and test it..