With DocBook, your world gets clearer. I will describe files such as docbook-example02.sgml. The following procedure illustrates how to make one:
Start a text editor such as emacs.
Type the contents of your file. When you are done, save the file using the key sequence Ctrl-x-Ctrl-s or the menu command File->Save Buffer.
If you did not supply a file name earlier, emacs will prompt you with the File to save in: message. Type a file name such as docbook-example02.sgml, then press Enter to save the file.
To check that you have actually made a file, use the ls command:
me@machine:~/docbook$ ls -l -rw-r--r-- 1 me me 1702 May 23 14:54 docbook-example02.sgml
When you have checked that you have a file, you can go on to Chapter 2.