Open Discussions
In Course Navigation, click the Discussions link.
Open Discussion
Click the title of the discussion
Reply to Discussion

To reply to the main discussion, type your reply in the Reply field.
Post a Message

Write your response in the Rich Content Editor [1]. You can add links, photos, equations, and/or media. If your instructor allows, you can also attach files [2]. Once you finish, click the Post Reply button [3].
View Your Reply
Your reply will be posted at the bottom of the discussion reply thread.
Here is a video on how to work with discussions in Canvas: