How can I view the letters?
You cannot, unless the teacher chooses to provide you with a copy. (Do not ask the teacher for it!)
The FERPA waiver that you sign when you set up the application systems in Naviance and the Common App says that you waive your right to see the letters. This step is regarded as the standard, since it shows integrity on your part. Colleges will not trust letters that they know have been screened by the student.