Creating a table of contents

A book commonly begins with a table of contents, so let's create one based on our numbered headings:

1. In our previous document, let's remove the options landscape and twocolumn.
2. Remove the setspace package, that is, delete this line:

   \usepackage[onehalfspacing]{setspace} 

3. Add the command \tableofcontents right after \begin{document}.

   Our code shall now look like this:

   \documentclass[a4paper,12pt]{book}
   \usepackage[english]{babel}
   \usepackage{blindtext}
   \usepackage[a4paper, inner=1.5cm, outer=3cm, top=2cm,
   bottom=3cm, bindingoffset=1cm]{geometry}
   \begin{document}
   \tableofcontents
   \chapter{Exploring the page layout}
   In this chapter we will study the layout of pages.
   \section{Some filler text}
   \blindtext
   \section{A lot more filler text}
   More dummy text will follow.
   \subsection{Plenty of filler text}
   \blindtext[10]
   \end{document}

4. Compile the code twice. Afterward, the first page of your output will contain this table:

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