On the nav bar, click the Activities menu, then select Discussions.
Do one of the following:
On the Discussions List page, from the context menu of the forum or topic you want to receive notifications of new posts for, click Subscribe.
Select a Topic from your Discussion List. Then, on the View Topic page, click Subscribe under the Discussion Topic title.
Select a Topic from your Discussion List. Then, on the View Topic page, beside the thread you want to receive notifications for, click Subscribe.
In the Customize Notifications pop-up window, select your Notification Method. If you do not have an email address set up in your user profile to receive notifications, in the Customize Notifications pop-up window, click the Add an email address in a new window link. Click the Enable email notifications link, then set your email preferences in the Email Settings pop-up window. Click Save.