Select a contact from your contact list to switch to the chat view. In the chat view, you'll see all messages between you and your contact as well as their current status.
To send a message, select the text box on the bottom of the page and type in your message. Send a message by pressing the Return key on the keyboard, or the Send button.
You can go back to the contact list view in two ways: Select the Contacts button to leave the current chat session open. Click the X button to close the current chat session.
Note that if you switch windows in Safari, the Google Talk window will become inactive and you will be signed out of Talk.