It's quite simple really. You either create or connect to a room by unique key, that you've chosen or received by someone. You also define your username. (A way to differentiate between chat participants)
The chatting room exists only as long as there is at least one participant. After that, the room will be deleted, but the room's key can be reused.
No you don't need an account. There isn't even option to login nor register.
No! the Room itself lives inside of server's temporary memory (RAM) and only has knowledge of your username. Furthermore, the messages are stored only on your browser tab, meaning, that once you refresh or close the tab, the messages will be gone.
Not yet. Currently the only way to communicate with each other is in form of text.