Launch your Google talk Application from the start menu or desktop shortcut icon.
Enter your Gmail ID and password to sign in with Google talk.
Once you are signed in, click on ‘+Add’ tab at the bottom left corner of Google talk application.
Now write ‘firstname.lastname@example.org’ to join the chat room.
Click ‘Next’ and then ‘Finish’.
If you want your friend to invite you to join a chat room then ask him to simply write ‘/invite email@example.com’. An invitation will appear on your screen from ‘firstname.lastname@example.org’. Accept the invitation to join the chat room and have fun.