To successfully give a TeacherMade Assignment to your students, they must already be enrolled in the Google Classroom. You cannot assign work to an empty classroom. If you attempt to check a class with no students, you will see an error on the screen indicating that you must first enroll students in the class in Google Classroom. If you click "Select Students" to pick which students will receive an Assignment and there are no students in that Google Classroom, you will see an error reading "No students found in this class."

You may need to talk to your Google Classroom administrator to enroll students in your Google Classrooms.