Adding A Video To A Website Page
First job create your video.
Video requires special hosting but thankfully YouTube.com offers the chance to host your website with an expert service.
(If YouTube.com is not for you Vimeo.com offers paid for option)
The simplest option is to add a new section and drag across the Big Buck Bunny example on.
If you click the blue box with the <> you can see the code which plays the video. Swap this out and swap your YouTube video in.