Each user type has a distinct set of privileges. Be sure to grant the appropriate privileges to enrolled course participants.
Professors have master access over the course functions.
This includes grading assessments, changing grades, enrolling students, assigning students into study groups, deleting items, and publishing tests. This includes the ability to develop test questions, verify grades, manage users, and many others. T.A's don't have the ability to create discussion forums. The grader access only permits access to the gradebook.