Notifications
Notifications will update you about the status of your documents and any actions or changes that might have been made.
The number in the upper right corner next to your user profile signifies how many unread notifications are currently pending. By clicking on this icon, you will be shown a detailed list of all your notifications. To dismiss them all, click on the Mark all as read button.
The Mentions tab only shows notifications in which you have been mentioned by another user (in comments).