Your class work that you see in blue with a "+" sign is a lesson or chapter. When you click on these links a dropdown of additional work will open up, and the "+" becomes a "-". Some of the dropdown contents will include web pages, assignments, and assessments.
Notice the Content Progress Indicator box below the Schedule button.
This will tell you if you have visited the assignment or assessment within the class. This does not tell you whether you have completed the assignment.
To move between pages in your classroom navigating you can press the "next" and "back" buttons provided in the top right corner of the page. Use these buttons to move to the next page of the class work, or the back arrow to review the past work. Think of these buttons as help for you to flip through the pages of an online book.