The course generally does not contain a news forum/forum "Announcements". The "Latest announcements" block only works with a standard news forum/forum "Announcements". If you want to use the block, go to the block "Administration" > "Course Administration" > "Edit settings". Under "Appereance" and "Number of announcements" enter a number greater than 0. Go to "Save and display" and you will see the news forum/forum "announcements". Please note that this forum only serves to provide students with information. Students cannot reply to posts. Moodle offers a number of other forums that you can create in your course.
Note: If a Moodle course or a forum is set to "hide", students will not receive e-mail notification messages when there are new posts.