Clicking on the link for any discussion takes the student into the forum. Clicking on a Discussion thread opens that thread in the forum. You can see, in the following screenshot, that the teacher started with the first post. Then, a student replied to the original post:

As Moodle supports an interactive, collaborative style of learning, students can also be given the ability to rate forum posts and the material submitted by other students. You'll find out more about forums in Chapter 9, Getting Social with Chats and Forums.