Permissions for users are defined by the Moodle site administrators only. Admin can see them at Site administration ->Users -> Permissions -> Check system permissions
It depends on the role you are assigning to that user for specific course. There are many roles available, However you can customize the roles by visiting "Site administration->Users->Permissions->Define roles".
The default roles available in moodle are Guest,Student, Teachers, Non-editing Teacher, Manager,Course Creator.
Kindly refer following link for more details.