Each course is different - some have prerequisites, and some don't. Take a look at your specific course’s recommended prerequisites on the course description page. If you do not meet a particular prerequisite, you may still take the course.
All required academic materials will be provided during the course, within your browser. Some courses may list additional resources on their course description pages. For supplemental reading material during a course, post a question in the course discussion forum to ask your classmates and course staff for suggestions.
And, of course, be sure to check out DemoX to get a better sense of the edX platform and how courses work.