How to write preface and postscript?

When writing the preface, we should pay attention to the correspondence with the text. You can write some philosophical words, either your own or those of celebrities. In addition, you can write some motivation or background for writing.

The postscript is similar, but the result is written. For example, a novel or report may have the later experiences of the main characters as a postscript, or it may be your own opinion on this matter, or you can write the writing motivation and background of this article.