To register on toone.rs, use this link: Registration
There's a one registration per hour per IP limit.
After registering successfully, you have a choice of an XMPP client to make. You can pick any that you prefer. For now, we'll focus on one - Converse Desktop.
After logging in, you can't see much. Press the hamburger menu next to GROUPCHATS. Then, press Query server, and then Query for Groupchats. Click on the one that says Public.
XMPP clients to peruse at your leisure: XMPP Clients
Generic web client: Converse Web