The Discussions homepage shows you an overview of all the forums and the accompanying topics that have been created for the specific course. In the Discussions List you can select to which fora or topics you would like to subscribe. 

To (un)subscribe to forum updates, click the fold-out arrow next to the title of a forum

• Click Subscribe/Unsubscribe 

 To (un)subscribe to topic updates, click the fold-out arrow next to the title of a topic

• Click Subscribe/Unsubscribe

The Subscriptions tab shows you a list of the forums, topics, and threads to which you are currently subscribed to receive notifications. It allows you to select how you want to receive notifications (in the form of an email) about discussions forums, topics, and threads to which you are subscribed.

1. Select whether you want to see all of your subscriptions or just those related to forums, topics and/or threads. Click Apply. 
2. You can select whether you want to receive the notifications in the minibar, as an email, or in your daily summary of activity below Default Notification Method.
3. You can select the notification method for each forum, topic, and thread separately.
4. Click Subscribed to unsubscribe from a forum, topic, or thread.
5. You can find more information about changing the settings of email notifications here.

It is also possible to adjust your notification settings by following the steps below:

1. Click on your name in the minibar.
2. Select Notifications.
3. Under Summary of Activity you can select how often you want to receive notifications.
4. Under Instant Notifications you can manage you wish to receive notifications instantaneously for all activities. This folder holds the option Discussions - new post in a forum, topic, or thread that I subscribed to in instant notifications. When you select this, you will receive notifications for any discussion update. 
5. Click Save to save all changes.