For more information about Discussion Forums, you can look through the information bellow or read Moodle's Support documentation
There are a handful of changes to the forums in 3.9
Whole Forum Grading- In Moodle 3.9 you are now able to grade a student’s collection of posts in the forum. This is in addition to the rating system that has been present in Moodle 3.5. You can learn to set up the Whole Forum Grading bellow.
Star a discussion - You can now star a discussion topic in a forum activity. This will bring that discussion topic to the top of an individuals’ forum, under any pined posts. Staring an topic is on an individual account and can not be done for the complete class.
Change in subscription icon – In Moodle 3.9 the option to subscribe to a form topic has changed. The system now uses a slide bar to indicate if you are subscribed or not. A blue slider bar indicates you are subscribed.
Locking a topic – Teachers can lock an individual forum topic to prevent students from adding anymore posts to that topic.
Creating an online discussion is a great way to continue learning outside the classroom. To create an online discussion, we can use the Forum activity.
If you are subscribed to a forum, you will be notified by email of every subsequent post to that forum. These emails allow you to stay informed when new posts are added. Depending on the number of responses to the forum, this could quickly fill up your mailbox. Fortunately, people can usually decide whether or not to be subscribed to a forum, unless the instructor chooses to force the subscription (see item below for how to unsubscribe from a forum).
Faculty can choose if the subscription to a Discussion Forum is Forced, Optional, Auto-subscribed, or disabled. Forced subscriptions prevent users from unsubscribing.
To change the Subscription Setting:
To unsubscribe from a forum:
In Moodle you can grade a Forum by rating individual post. This is a more granular way of grading then the Whole Forum Grading discussed below.
In Moodle 3.9 forum grading now has two options. The current rating option where you can rate individual posts and the New Whole Forum Grade option. This option allows you to grade the student's overall contributions to the forum.