Notification Settings are the settings that deal with your notification preferences. Notification settings can be found by going to My Account and scrolling below My Account settings.
Notify me about new comments: Enabling this notifies you whenever someone comments on the tasks and projects that you have been assigned to.
Notify me when I'm assigned to something: Enabling this sends an email notification when you have been assigned to a task, project or client.
Notify me when something is completed: Enabling this notifies you when a project or task you have been assigned to has been completed.
Remind me when something is starting or due: Sends a reminder when a project/task is starting or due.
Enable in-app notifications: Enables the notification section of ProProfs Project.
Notifications: This drop-down allows you to decide whether you'd like to send notifications to others in the tool.
Suggested Reading: My Account Settings