You can manually enter grades into Moodle's Gradebook using Grade Items.
First you want to get into Moodle's Gradebook. Under the Settings Block click on Grades.
This will take you directly into the Grader Report.
You will see your list of students enrolled in your class, as well as any grade items you have created.
In the top right corner, turn editing on.
You will now see a box in which to input your grades under each grade item. You can click in each box or tab though and enter your grades for each student.
As you enter a grade it will save automatically when you move on to the next box.