The previous examples of TeX source code are far from cover all the useful TeX macros and features. It is surely beyond the scope of this book to teach you how to use TeX. To learn more about TeX, you might want to try some of the following books:
Donald E. Knuth: The TeXbook, Addison-Wesley, reprinted 1993 – if you want to become a TeX guru, this is the right book for you.
Paul W. Abrahams, Karl Berry: Tex for the Impatient, Addison Wesley 1990 – a simplified TeXbook. Each concept and command is explained in a separate entry with many helpful examples. It is available online at http://tug.org/ftp/tex/impatient/.
Michael Doob: A Gentle Introduction to TeX – a very easy-to-understand tutorial for beginners. It is available online at http://ctan.tug.org/tex-archive/info/gentle/gentle.pdf.