If you want to understand more about your grades, the "Progress Reports" page (1) is the best place to go. (You can also hover over or click on your grade on the "Grades" page.)
Be sure to choose a specific course and grading period (2). Once you do this, you'll see a summary of your assessments (or your standards, depending on how your school does grading). Pay attention to the columns that list "Points", "Out Of", and "Points Dropped" (3). These columns show you which assessments or standards you've done well on and which ones you've done poorly on, compared to all of your other results.
You can use these columns to see which results are hurting your grade the most. The more points dropped, the more this negatively impacts your grade. You might want to identify which results are costing you the most points and ask your teacher if you can make up the assessment to bring your grade up and your missed points down.