You can access grades when you want to check how you are doing academically. Here you will be able to see your grades on the individual assignments that you submit. If your instructor makes any comments about your assignments, you will be able to view them here as well. By selecting 'view stats' for the individual assignment, you may be able to see the class average, and a graphical representation of your mark in comparison to others.
When your grades are published, they appear on your personal Grades page in the course. Depending on how your grades are set up, you might also be able to view comments and overall class performance statistics.