Something is happening inside your Huler Hub! When someone gives you Kudos, shares a collection with you, or when a tile has been updated, you will receive a notification.
You can see how many notifications you have in the bottom left hand corner of the Hub. The icon will be highlighted by the number of notifications you have unread:
Clicking on the icon will open the notification view, displaying the detail of each notification message, which can be clicked in order to navigate to that area.