You Can join our IRC by clicking this link: ircs://acm.umn.edu:6697
If that doesn't work, and you use the weechat irc client, you can connect by typing (or pasting in) these commands:
/server add acm acm.umn.edu/6697 -ssl
/connect acm
/join #general
The most active channel by far is #general. Most of the time when people say "the irc", they mean #general.
you can enter /list once you are connected to the server to see all of the channels.
Most of the channels outside of #general are channels that are connected (bridged) to the discord.
The briged channels other than #discord-general are password restricted, as they are member only.
For access to these, ask an officer or someone in the IRC.