What is IRC?
IRC stands for "Internet Relay Chat". It's basically a chatroom service. There are many chat servers, hosting different channels. You can think of each channel as a separate chatroom. To join the channel, you need to know its name and the server it's on.
You can find out more about using IRC here.
Hackspace IRC Details
The Hackspace channel is #leedshackspace on the irc.libera.chat server.
Since before 2010, the Hackspace IRC channel has been hosted on the freenode network. Sadly in 2021, the nameservers were sold and a hostile takeover of the entire Freenode network was underway. In June 2021 the final straw: the new freenode controllers deleted all of the channels and accounts that had been active on the network. At this point our hand was forced and we've migrated over to Libera.Chat which (apart from my dyslexia finding impossible to spell) is essentially the majority of admins and communities from the old freenode network.