Begin by clicking on "course admin" in the blue navbar, then scroll down and click on "assignments." Scroll down to the assignment you'd like to grade and click on the caret next to it and then click "view submissions."

Scroll down and click on the student/submission you'd like to grade.

Enter your grade/feedback, then click on the blue "Publish" button if you're ready or "Save Draft" if you want to publish it later.

When you're ready to publish feedback, in the "submissions" screen, select all students to publish grades/feedback to and click on the blue "Publish Feedback" button.