Click on the bell icon on the upper right corner of the screen, under your name. A My Notification(s) window opens and you get an overview of the unread notifications that you received.
The red circle indicates the number of unread notifications that you have and, when clicking on an item in the list, you open a specific notification. Once you have opened a specific notification, it will disappear from the unread notifications list and you will find it back after clicking on Manage all notifications:
Click on Manage all notifications at the bottom of the list to get into the My Notification(s) section:
The Inbox tab gives you access to all the details of the notifications that you have received. You can also mark notifications as read, unread or delete them: