The format is online, but real people work at both ends as teachers and students. Communication is key to the experience.
How are you to contact your instructor? Some instructors use the Virtual Office option, a link found on the main page of your classroom site. Some prefer email, others the phone. Check the course syllabus to know the preferred method.
When corresponding with your instructor, post within your message the following: your first and last name, class and section number, phone number, and your campus of origin. Doing so helps your instructor to quickly identify you as the sender.