What are the differences between an announcement and an Inbox message?

Announcements are sent to the entire course and can not be restricted to a section or particular student. A message can sent to a course member, set of course members, section, group or the entire course. See the chart below for a quick comparison. 

  Announcements Inbox Messages
Recipient options All course participants  All course participants
Specific sections
Specific groups
Role based
Location of content In course site Outside of course site
Notifications ASAP by default ASAP by default
Can the whole class see the content?  Yes    No, only those the message is intended for
Can be deleted?   Yes (can't retract email notification)   Only from your view 
 HTML/ Rich Text Editor option?  Yes No 
Can students respond?  Yes/No - instructor can restrict students from responding Yes 
 Add multiple attachments?  No, but can embed multiple downloadable files  Yes
Draft mode? Yes - delay posting (can edit up until the post date and time) No 

To create an announcement, follow the steps in Canvas's How do I make an Announcement in a course? guide.

To send a message to your students, please see How do I send a message in Conversations? for step-by-step instructions and screenshots.