Generally speaking your course page, located under My Courses, will include all the relevant course materials for you to be able to study the course.
The course materials provided are sufficient enough for you to be able to complete the course. Everything you need complete the course assessments/assignments will be contained within the course text.
However, if you wish to do any optional additional reading outside of the study text, it is entirely down to you and will inevitably boost your knowledge on the subject matter in question. Though we should state additional reading, unless explicitly stated, is not mandatory.