For information about how to start a course, see How do I start my course?
After you have enrolled in a course, the course is posted on your edX dashboard. The course start date is located below the course title.
Until the start time has passed, you will be unable to access the course. Once this datetime has passed, the Begin Course button will activate.
Depending on your timezone, the start time may be later than you expect. If the course is unavailable on the start date try again later that day.