You can use Announcements to communicate with your students however it does have limitations in that Annoucements won't go out until after a course is published. Students should see the announcement when they login to their course on Canvas but notifications will only go out to students if they have their Annoucement Notifications turned on. If you want to use Announcements in Canvas you may want to encourage to turn on their Canvas notifications.
Email may be a more reliable method for contact your students but it's a basic email inbox made to send an recieve messages. You can schedule messages to go out and you may not want to attach files.
