Once your class is created, you will need to add one or more teachers to the class and add class members. To add a teacher to a class you must start to type the username of the teacher you want in the "Assign a teacher" to this class search box.
This will search the list of all of the users who have been given the role 'Teacher' across Teacher Dashboard. Either click on the name of the user or press enter to add the user as a teacher.
See the add Users section for more information on setting up users as teachers.