XMPP typically (and on this server) runs on port 5222. It requires a chat client for XMPP protocol chats. XMPP protocol means a software standard and has allowed the creation of a huge network of people chatting using the protocol. It is a well established and very extensible tool that many open source projects, as well as not open source, have been made from to use.
XMPP stands for Extensible Messaging and Presence Protocol. If you've ever use IRC before, or Slack or AIM, ICQ, it is one of those kinds of things. It's used for collaboration purposes and chatting amongst other various folks of the XMPP realm, such as these uses.
HardTeckno.com is using an XMPP server to give hardcore rave music fans a place to rant and rave about hardcore/hard techno/gabber/hard electronic. We also welcome other types of conversations such as allmusic, programming, web dev, dev ops, computing, AE and cool stuff
In order to access the chat rooms you will require a "JID", or Jabber ID, and thus you will have to create an account on a chat server (there are lots of other XMPP servers on the web). This is done with a chat client or sometimes websites have their own web register on their site. There are several clients available and it depends on what operating system you're using. Also it can highly depend on preference. You can look up what XMPP chat client you want on google or check out these links: