Edit->Preferences->Networks->choose my network->Edit->"Users and Channels" tab of "Network Properties"->"Automatically Join Channels" List. This list has a field for a channel's key.
Edit->Preferenc es->Networks- >choose my network- >Edit-> "Users and Channels" tab of "Network Properties" ->"Automaticall y Join Channels" List.
This list has a field for a channel's key.