All of your courses are listed in the left-hand panel of your homepage. Selecting a course will show you all the lessons and modules (groups of lessons) that are available for you to work through. For example, this student has access to the Marine Invertebrates module, and Antarctic Invertebrates and Phylum Cnidaria lessons.
Note that single lessons are indicated by a dog-ear in the top right corner of your image, whereas modules show the full image.
Selecting a module will show you all the lessons within that module. Selecting a lesson will open that lesson for you to complete. Selecting the "Back to [Course Name]" button will take you back to the course homepage.
For more information on lessons, click here.