Before you start chatting in google talk, you must add the person you want to chat to google talk.
For contacts already in your Friends list:
- Scroll over your friend’s name, and click invite.
- Verify your friend’s email address in the dialogue box that appears, and click Next.
- [advt]Choose to send a standard invitation to your friend, or customize the message by entering text in the text field.
- Click Next.
- Click Finish in the dialogue box that appears confirming that your friend was invited.
For contacts not in your Friends list:
- Click +Add at the bottom of your Friends list.
- Enter the email address of the friend you’d like to add.
- If you’d like to add more than one friend at a time, just make sure to separate their email addresses with commas.
- If the friends you’d like to invite are listed in your Gmail Contacts list, click Choose from my contacts… after clicking +Add.
- Click Next >> after you’ve entered all the friends you’d like to invite.
- A dialogue box will appear to confirm that your friends were invited to Google Talk. Click Finish.
If you’re a Gmail user, new contacts in Google Talk will also be added to your Gmail Contacts list, and vice-versa. Keep in mind that removing or blocking someone from your Google Talk Friends list does not affect your Gmail Contacts list.[source]