Grader is a root-level feature that allows you to grade multiple responses and even multiple classes in the same place.
Click on Grader in the main tabs at the top of your page to show a list of all your active courses. From there you can select assignments in each class and grade each student's responses. For more information on using Grader, see our Grader playlist:
Gradebook is a class-specific grading tool that functions like a traditional gradebook. Each assignment is listed, and each student's responses are available for viewing.
Click on the plus sign (+) in the applicable assignment column and to the right of the name of the student. This will direct you to the completed assignment, and where required, will include student uploads.