"User Guide" for Talk Android?

I’m using Talk successfully with my family. I maintain a Nextcloud server on DigitalOcean. I use the Android Nextcloud and Talk apps, and my family all use the iphone versions of those apps. The other day my sister said, “better video than facetime,” so that’s good. (We also use the app in the web browser, so I’m glad to see Safari will be supported in Nextcloud 16/Talk 6.)

But where is the “user guide” for the Talk app?

I frankly find the Talk Android app rather incomprehensible. There seems to be a concept of “Conversation,” and within a Conversation, a concept of “messages” and a “Call,” but none of that is explained anywhere I can find. (Video call? Voice call? We can make both work, but how are they related to a Conversation, and what happens when some participants have video and some only voice?)

There’s a “+” in a circle on the main screen, but what am I +ing? A Conversation? How long will that Conversation stay around? Can I have more than one Conversation active? (It keeps saying “You left the call.” Really? So what is left of the Conversation?)

When do others in a Conversation get a notification that I sent them a text message, that I’m trying to start a voice call, or a video call? I mean, obviously we’ve made it work, but where is that spelled out in concise, concrete text for me to read and undertand?

And when I start a voice call, why the HECK does the Android screen go completely black? Not even a list of the other participants with their status, disconnected, connecting, muted, etc. Not even an obvious way to restore my phone’s soft “back” and “home” buttons. And when I get the buttons to appear, does “back” kill the voice call? It seems to kill the voice call. Where are such details described?

Look, I’ll write a user guide, if that’s what it takes. So is this the right place to ask questions about un-obvious behavior? Do I need to go read the source code to figure out the details and understand the rationale for the UI choices the developers made?

Looking forward to using Talk more, if I can learn enough that it’ll stop surprising me and frustrating me at every tap. Thanks!