At the top of the page, in between the "Help" link and the yellow "Find Projects" button, you'll see a little black bell icon. If you click on that, you'll see your most recent notifications.

To see the project that a notification is referring to, simply click the notification text. You'll be brought to that project's page.

You'll notice that the notifications in your list that have already been clicked on are no longer in bold text. You can tell which notifications are unread because they're still in bold.