Teachers and teaching support can create an announcement to share important information with all students and instructors in a course. By default, an announcement will be posted to “All sections”, i.e. everyone in a course.  A course announcement can also be posted to a section of a course. Please see examples from the screenshots below.

"Post to" in an announcement

Post to all sections

Post to a section in an announcement

Post to a section

In comparison, global announcements are created by our Canvas admins and they display on the top of Canvas dashboard. 

Global announcement

 Global announcement

You can dismiss a global announcement but it won’t be deleted for you or other users. The Global announcements page shows the global announcements that are currently dismissed and the announcements posted in the last four months.