Docs/tutorial on the new 'cast' row in Lovelace?

Is there a source for concise documentation on how to use the new ‘cast’ feature described in the blog post (URL below), which will let me display a HA view on a Chromecast device (that’s attached to an old display panel)?

While I did get a view defined in my HA instance, and an entities card and a ‘cast’ row setup, in the UI it appears with the phrase: “Cast requires HTTPS”.
What has me stumped is where/how to specify the URL, and to what should it point? (I do have a nabucasa paid subscription)

The only doc I can find are at https://www.home-assistant.io/lovelace/entities/#cast
but it doesn’t indicate where I should supply a URL, or how to indicate which device to cast to.

All other searching for this has only led me to posts and comments from people who seem to have it working, but none say exactly how.

This is the announcement that I referenced above:

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