Hi el_gato_conbotas
To answer your question, when you are on the prepare step, you don't read at all. In fact the reading material, say a book, is closed and in front of you. Prepare means preparing yourself. In simple words when you prepare you are entering the Flow State. The steps which you need to perform while preparing are given in the PhotoReading book.
Its only when you are in the preview step that you start reading the material and this does not imply that you read the material from cover to cover. You just read some specific portions, once again mentioned in the PhotoReading book, to have an overview of the book and understand the structure of the book.
I hope I have been of some help to you.
God bless you.
Kind regards
Vaibhav Sharma