How does headings and subheadings affect a text?

It gives the reader a notice about what the text it is a about. This could be to see if the reader of the text is interested in the text. Sub headings gives the reader a notice about what the reader will find in that part of the text.

Well it tell you what you are about to read if you have a heading and subheading that tells you too much the reader will not read because they know from the heading and subheading to get a reader interested in the story have a good heading and subheading to pull them to the book