It’s just there and under the same domain. Otherwise, it’s a completely separate system that instance users can sign up and use. Maybe in the future they can both use the same OIDC login, but I don’t think Lemmy supports that yet.

The UI we use as our default has Peertube integration, so any videos shared from this Peertube instance (or any other) will show as inline embeds within the Lemmy client.