The course discussion board is a great tool for interacting with your students and checking in on progress within the course. Your first step should be to a look at this support article on the basics of using the course discussion board.
One thing to keep in mind is that as an instructor, anytime you create a post on the discussion board, a notification will be generated for all students in the course. So you can use the discussion board as an announcement system for students. This is only true when you post a message, not when you reply to an existing message. When you reply to an existing message, only the author of that message is notified.
For more advanced topics on the discussion board, please see these related support articles: