Most universities are set up in our system so that students purchase courses via our built in e-commerce.  In this case, log into the mbaprepworks site and click on the, "Go to Shop" button located on the right side of the page under the, "Buy Courses" header.  If you are on a mobile device click the < on the right side of your screen to expose the right column of the page.  If you log into the mbaprepworks site and there is no, "Go to Shop" button then you purchase the courses from your university and your adviser should have information on how to purchase a course.