What is the difference between Announcements and Discussions?
Announcements are designed to allow instructors to deliver information out to an entire class. Discussions are designed to allow interactive communication between two or more people within a course. Instructors do have the option to allow replies to Announcements. Also, one person can use a Discussion to communicate information to an entire class. The main distinction between the two is that Announcements are intended for broadcasting information while Discussions are designed for participation in a public conversation.
Announcements are a way to communicate important information to a large group of people. It does not require a response, like a Conversation, which eliminates the risk of spreading personal information. Students can respond to your announcements unless you close the announcement for comments.
Announcements and Discussions will both appear in the Course Activity Stream and on a user's Dashboard. Announcements are indicated by a megaphone icon  and Discussions are indicated by a bubble icon . Next to the icon, Canvas will display the number of Announcements or Discussions, along with a link to the course(s) where the new Announcement or Discussion has been posted.
Students can still reply to Announcements, but replies will not appear in the Conversation Inbox.
Additionally, students can subscribe to Announcements via any external RSS reader. The link to the announcement feed is at the top of the Announcements page.