...
Instructors use announcements to communicate time-sensitive information and course updates. These are always in an announcements area, but may also be sent directly to your email. Look for the Announcements link on the course menu or in the Tool Panel.
...
In discussions, you can share thoughts and ideas about class materials. Participants don't need to be in the same location or time zone, and you can take the time to consider your responses carefully. Look for the Discussions link on the course menu, in the Tool Panel, or Discussion links in course modules.
Course Messages
You can view messages in each of your courses. If allowed by your institution, you You can also create and reply to messages . If allowed, you and from your instructors can send messages to each other, multiple people, or an entire class for reminders, quick questions, and social interactionsand other students.
Messages activity remains inside the system. You can't view or send messages outside of your course.
...