Once you have downloaded and installed pidgin:
- Accounts > Manage Accounts
- Add...
- Protocol: IRC
- Username: your preferred nickname (please use your real name)
- Server: your irc server, eg irc.freenode.org
- Password - leave blank
- Add
- Close (the "Accounts" window)
Back in the main pidgin window:
- Buddies > Join A Chat...
- Account: the one you just created
- Channel: #favouriteroom, eg #pidgin
- Password - leave blank
- Join
In the new chat window for the chatroom:
- Conversation > Add...
- Tick "Autojoin when account connects."
- Tick "Remain in chat after window is closed."
- Leave everything else as defaults
- Add
Now when pidgin launches you will have "#favouriteroom" in your buddy list, and you can double click to open the chatroom.
You may also want to make pidgin start when windows starts;
From the main window:
- Tools > Plugins
- Tick "Windows Pidgin Options"
- Configure Plugin
- Tick "Start Pidgin on Windows startup"
- Close
- Close (plugin window)
I also recommend enabling the Markerline plugin to help see what is new in the channel.