Looking for a listing of EdX courses?
Click on the green Enroll Now button on the right of the edX course information page. You must pay if you want a certificate.
You can then work through the course materials and complete assessment items. Earn a certificate by gaining the required number of marks for the course.
Required pass marks can vary from course to course. Some courses have limited chances to re-do quizzes and exams, so think carefully while answering the questions.
Financial aid for up to 90% of the certificate fee is available for eligible students. See https://support.edx.org/hc/en-us/sections/115004147627-Financial-Assistance