This document is an example of a book, and a book generally contains chapters, which may contain sections. A paragraph of text can be put in a para tag. There are lots of examples of that in this book (see the appendix called DocBook SGML source).
When you want text to appear with its layout intact (spaces and newlines kept where they are), you can use the literallayout tag. Note that Tab characters are not expanded. If you also would like a different font for the listed text, you might want to use the programlisting tag.
The following sections are for example only, and may not actually mean anything.
This shows how to handle images for both print and web display; each format is included in one mediaobject so the stylesheet, when faced with a limited subset of formats for the current output media, can select the best fit.