Embed YouTube Videos
Copy the video's link and paste it onto an empty line in the editor. It turns into the video straight away, and it plays there while you write, so you can check it is the right one before you publish.
You can also press / and pick Video or embed if you would rather paste the
link into the block itself. Either way works, and both accept a normal
youtube.com/watch?v=… link, a youtu.be short link or a Short. You do not
need an embed code.
See Video and embeds for the full list of what plays inline.
Create Video Posts
While often a short video embed is enough, sometimes your post is more about the video than about the blog. In that case, you can create a video post that will have a large video playing on top.
To add a cover video to your post, first find the Background Image selector in the editor sidebar (under "Media"). Click the camera-switch icon to switch to the cover video selector. Now, enter a Youtube.com link to a video (e.g. https://www.youtube.com/watch?v=A1t6G5m9s7g) and click "Add video".