All start dates will be described on the applicable course page.
Your selected course may have a limited number of course dates where you must be ready to attend, either in person or online. Such courses may also have fixed completion dates for assignments or other assessments.
Alternatively, your course may be 'self-paced', where you may begin at any time and complete all assessments at a time of your choosing. While self-paced, assessments will generally need to be completed within a certain time-frame.