If you'd like to receive notifications (Alerts) for Conversations, it helps to know what you are subscribed to and when you will, or won't, receive an Alert.
(For more information on Alerts, you can visit here!)
Conversations at the Forum Level
There's only one thing to do here: Subscribe or Unsubscribe. If you are Subscribed, you will receive an Alert if a new Conversation is added to this Forum.
Conversations at the Conversation Level
Here, if you choose to subscribe, you will receive an Alert if a new post or reply is made on this Conversation.
So - in the example above, I would not receive an Alert if a new post is made to the "Announcements 7.2" - even though I am Subscribed to the "OnSemble Showcase" forum.