Right before the course starts:

Send an email to everyone on your student roster introducing yourself, providing contact information for yourself and the URL of the course website, notice of when the course will actually start, and a bit about your expectations. 

Your course will have a Blackboard website automatically assigned to it. This is one of the best ways to post course information. Be sure to test out your Blackboard site before your class begins. Be sure to let your students know how to participate in your course.