If you still don't know what google talk is , that means you are not google mail ( gmail ) user. While mailing from gmail you can chat with friends. Google talk program is an client which allows you to chat with friends without beeing in gmail.
more about it: http://www.google.com/talk/
*text* - Bold text
_text_ - Italic text
shift + enter - break line ( new line without sending message )
You can always make suggestion on Google Talk if you dont like something or you would like to see something.. here: