In your Course Menu, you will likely find a link for the Discussion Board (If you do not have a link to the Discussion Board, you will need to add a tool link to the Course Menu first). However, you will need to create forums for this discussion board. When you create a forum, you can set the settings for that thread including availability, allowing file attachments, allowing authors to delete posts, and grading.
Instead of grading an entire forum, you can grade user's individual threads. This is useful for more detailed responses or participation grades.
When you create discussion board threads, settings you choose will only be set on that particular forum. So, if you want to grade one forum but not another, you do not have to choose that setting.