To add a video screen that’s bigger than an inline video (see below for actual size),

select Video block from the panel at the top of the body block

In the Edit video block, put the Youtube url into the appropriate field, then click OK

and you’ll see the video block in your page block

None of the fields in the video block are mandatory; you can leave them all blank and the video will appear on the page when you save it. But...

If you want to use a different image that sits on the video screen before the user clicks play (instead of the default utube image), put your cursor in the image field and click E in the panel at the top of text block ​then either select your image from the media library or upload a new image in the same way you would if you were adding a feature image (see Feature image). 

You can also add title, subtitle and body text to a video block. The video can appear on its own, but if you need some text below it, you can add it here, without needing to open a new text block.

NB use sparingly, at least until we get the ability to select different sizes for these components, as this block is really quite big. See below for an example of a video block without any title, subtitle or body text.