There are several ways to grade using Brightspace. Going to Grades is NOT typically the best option.
Quick Eval - best for individual assignments (under Help & Resourses)
Activities - best for groups and filtering by section
Discussions
Assignments
Quizzes
Grades - best for giving many the same grade/feedback simultaneously
Enter Grades: use Standard or Spreadsheet view
Manage Grades: item > Enter Grades
Brightspace Grading Recorded Session (38:21) - Session from CID
Grade Using Quick Eval (Google Doc)
Grade Discussions (Google Doc)
Everything you could possibly want to know about Grades - Google Doc from Portland CC
Exempt Students from Grade Items - The University of Arizona