You can connect using a client like mIRC or the "In-game chat" link at the top of the website.
Port: 6697 (SSL)
Password: Pathis Orb Minecraft
Why Internet Relay Chat?
1. It's a free, open-source protocol that can be hosted or accessed anywhere. There is a multitude of server and clients, and anyone can make a new one.
2. Resource usage of IRC clients is much lower than Discord; you can run a command-line IRC client in less than 10MB of memory (even graphical clients are relatively small), compared to Discord's hundreds of MB.
3. IRC is truly server-owned. A Discord "server" is never really your own -- it's technically owned by Discord and subject to their terms.
4. It's been around for decades, and it's still being improved and updated. It's probably never going away.