On the top bar, there is an antenna icon representing your Notifications. If a number appears next to the antenna, it means that you have unread notifications. The number in the circle indicates the number of new notifications. If there is no number next to the antenna, it means that you do not have new notifications.
Click on the antenna to see your latest notifications:
You can decide to click on the "See All Notifications" link which will redirect you to a page where you can see and delete all of your notifications. You can also directly click on "Clear All" to remove the latest notifications from this information panel.