Not all edX courses have exams; many do, but not all. When choosing a course, it's a good idea to check the exam and study requirements, as well as any prerequisites.
Of course - you can "audit" any edX course, which means you can study alongside other students using the same content, tools and materials, but you're not focused on grades and might skip the exams and assignments.
Follow this learning sequence via the links above to understand more about how we grade your work and track your progress.