Most of IRC is on those 'channels' (#whatever). and most channels (at least back in the day) were public, so you could just go to #books or whatever. For example, I spent my formative years on #uiuc, where there was a healthy community of 50-100 people from the university I was at. Newcomers would stop by on a regular basis and ask a question or just start chatting or troll or even grief--there were kickbans and scripts and bots to help manage larger communities.

Also these persistent channels are created just by joining the channel with that name; they disappear when the last person leaves. Notably, the first person to join a chatroom gets "operator" status, and thus the rights to change channel settings and kick/ban people etc. So there evolved a culture of bots, who would sit in channels with op status and 'occupy' it in case someone came along; these bots had op status themselves, and were programmed to auto-ban certain users or even domains, and auto-op their owners and their owners' friends. slap me summa dat +o.

And of course, there were the bot wars and the attempts at deliberate netsplits to try and steal op status, which were fun games for the script kiddies, but would really take the piss out of your evening chat when they would come by.