To enter gradebook grades, go to Grades >> Gradebook >> Grades. Grades can be entered in three ways here.
Selecting the All view from the drop-down enables the teacher to enter grades for the students in all assignments at the same time.
If you want to enter grades for a particular assignment, select that assignment from the drop-down list and grade the students for the selected assignment.
Also you can click on a student's name from any of the views and enter grades for the selected student in all his assignments.
The Totals View shows the assignment score total with respective letter grades.