Donna,
If you post an announcement before the course is published students will NOT receive a notification about the announcement. It will be there to access in the course once the course is Published, but no announcement will ever be sent. Also of note, when you embed media such as an image or video in an announcement it will not be displayed in the notification email. Students will need to view that announcement in Canvas to access the media (there is a link to do so in the announcement notification). I usually tell instructors that if they plan to include media in an announcement to indicate so in the text of it.
One trick I have seen people do is to Publish their course, post an announcement or send a message through the InBox, and then unpublish the course. This works to get a message out but because of my explanation above would not work well to get a video out to them.
Rick
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.