I want to chat with other Ubuntu-ers but I'm lost on how to do this properly. Do I have to sign up anywhere? Is there only one Ubuntu channel?
Step by Step Guide to connect to an IRC room
From the global menu Edit - Accounts click the + button and change the chat to IRC as shown. Enter your nickname and click the Login button.
After a few seconds you should see the green icon now blinking indicating that you have connected to the server
Next action is to join a Room.
Enter the room name - all rooms start with # e.g. #ubuntu. For a list of Ubuntu rooms, see the link below.
After joining the chat window should open displaying all chat-room users and the current chat activity.
IRC channels of ubuntu are on Freenode AFAIK. You can use empathy or any other irc client.
You don't really have to be registered to irc to use it. But some channels only allow registered users. You can choose a nickname/username and enter. If it is already taken you will be allocated a guest id otherwise you can register the same nickname.
You need to have telepathy-idle installed, and you need to have at least one non-IRC account (see Gnome bug #596086 for more details). Then you can connect to the IRC server by creating an account, and join a channel by using the Room > Join room dialog.