The "Grade Me" block gives instructors a course-wide view of all the student submissions that require grading.
For a busy Teacher, having a heads-up display of all the assignments, lessons, or quizzes that require marking can be pretty handy.
The Grade Me plugin is designed to work with Moodle Groups. For this block to show you the assignments submitted by your students, you and your students must be members of the same group. You'll only be able to view the assignments submitted by students if you both belong to the same group.
This article gives a detailed description of Grade Me's features and use: