Get through your email fasterEmail is great, except when there’s too much of it. Priority Inbox automatically identifies your important email and separates it out from everything else, so you can focus on what really matters.
Automatic sortingGmail uses a variety of signals to identify important email, including which messages you open and which you reply to.
Sections keep you organizedIncoming email gets separated into sections: important and unread, starred, and everything else. Don’t like these? Customize them.
Predictions improve over timeOver time, Priority Inbox gets better at predicting what’s important to you. You can help train it using the buttons.
For more info on this :
Please visit : http://mail.google.com/mail/help/priority-inbox.html