Discussion Boards in SharePoint lets you to discuss key points, post your questions, attach files, reply to questions and marking the answer as best bet as well. There are various views available in Discussion board 2013 are
1.Flat
2.Public
3.Management
4.Threaded
Flat View - Flat is the default View that you see in above screens.
Management View - Management is the view for Admins to see the Reply statistics for this discussion.
Threaded View - This displays the discussion in the form of old Discussion view (of SharePoint 2010).