From the discussion list (on the Home page or from one of the site categories discussion lists), click the subject of one of the discussions to open it.
At the bottom of the first part of the discussion, click the More Options ellipsis (...) and then, on the menu that appears, click Alert Me.
On the New Alert page, modify the title of the alert if the suggested title isn’t specific enough. This title is used for future alerts notifications.
If you have library administrative privileges via the Manage Lists permission, you can also add additional recipients for the alert notifications.
Specify a delivery type for notifications.
Specify which types of changes to the discussion should result in a notification being sent.
Type additional filter for the notification.
Specify how often notifications should be sent.
Click OK to create the alert.