Notifications are updates to projects you're involved in, and are sent in-app (via the bell-shaped Notifications Icon) and via email, when preferred. Notifications can be set on two levels: project-specific notifications, and global notifications (Enterprise users only).
To view your notifications in the app, click the Notifications Icon in the top right bar. It'll have a red badge with the number of unread notifications on it if you have new notifications to look at.
You can filter your updates via the Filter Icon. You can also clear your notifications by clicking the Gray Checkmark Icon.
Find out more about managing your Notification preferences.