Group chats in bitlbee using most Jabber servers
See GtalkGroupchats for Google Talk accounts specifically.
1. First of all, add the account if you haven't already, eg:
account add jabber firstname.lastname@example.org [password]
2. Then add the chatroom using the chat add command. Most jabber room names take the form email@example.com.
chat add [account] firstname.lastname@example.org
You can optionally append a different name for the channel to be created; it will default to the room name. [Aside: chat add is shorthand for a bunch of channel commands.]
3. If the chatroom is password protected, set the password:
channel [id] set password [password]
4. Activate your accounts
5. Join the channel now associated with the group chat (chat list if you are unsure)
Ad hoc chats
If you are running bitlbee 3.0.5 or above, you can create ad-hoc chats with people using the standard approach for all protocols of /join #something and /invite people.