Before accessing a particular TWEN course, you have to add it to your dashboard.
To do so with the old UI enabled, click the arrow next to the Manage Courses tab on the upper righthand side. Then click "Add Course." Then, search for the course you're looking to access and click "Add." Finally, click "Go to Course" to access the course page.
To do so with the new UI enabled, click the + symbol on the upper righthand side. Then click "Add Course." Search for the course you'd like to access, check the box, and click "Add" Close out of the search menu and click the course title to access the course.