If you are creating a single class (not creating multiple classes) and you haven't yet created the teacher or room that will be associated with the class, you can do this from the Class Builder Page.
Simply select 1 New Instructor (or 2 New Location) and create and save the new instructor and/or location/room. Be sure that you are indicating that the new staff member is 3 a teacher.
Also, remember to edit the instructor/location details. You are able to create an instructor and a location here, but you are filling in information for limited fields. Go to the instructor and location/room details to complete the information.