To add a contact to your friends list they must have a valid Gmail account, as well as the application installed on their desktop, or mobile device. Contacts cannot be imported into the Google Talk application on the device as there is no option, and both conditions would have to be met (valid Gmail account and the program installed on their desktop or mobile device.)
You can better manage this from your Gmail email account online; however on the device you would have to manually invite new friends to join the Google Talk application. *** This is also provided that they meet both Gmail account and program install conditions.
Below I have given a link to the support site for Google Talk. This site will give several “how to’s” as well as troubleshooting.
I hope this information was helpful.