Select the 'Classes' tab on the top of your page.
Select a class name.
Select the 'Assignment' tab, and find the column that says 'Submissions'.
In the row of the assignment that you wish to view submissions for, Click the down arrow below the 'Submissions' column.
You will now see a list of all student submissions. Select the 'Answers' button of the student's submission you'd like to grade.
NOTE: you can only view student submissions if they have turned in the assignment. If they have turned it in, you will see 'Turned In' above the 'Answers' button. If they haven't turned it in yet, you will see 'In Progress' above the 'Answers' button.
To grade the entire assignment, click 'Grade' on the student's submission you wish to grade.
You can leave a grade or, if the deadline has not passed for the assignment, you can leave a remark or feedback and click/tap the Return button at the bottom to have the student submit again.