Sectioning
Sectioning commands provide the means to structure your text into units:
\part
\chapter 	(report and book class only)
\section
\subsection
\subsubsection
\paragraph
\subparagraph
All sectioning commands take the same general form, e.g.,

\chapter[toctitle]{title}

In addition to providing the heading title in the main text, the section title can appear in two other places:
The table of contents.
The running head at the top of the page.
You may not want the same text in these places as in the main text. To handle this, the sectioning commands have an optional argument toctitle that, when given, specifies the text for these other places.
Also, all sectioning commands have *-forms that print title as usual, but do not include a number and do not make an entry in the table of contents. For instance:

\section*{Preamble}

The \appendix command changes the way following sectional units are numbered. The \appendix command itself generates no text and does not affect the numbering of parts. The normal use of this command is something like

\chapter{A Chapter}
…
\appendix
\chapter{The First Appendix}

The secnumdepth counter controls printing of section numbers. The setting

\setcounter{secnumdepth}{level}

suppresses heading numbers at any depth > level, where chapter is level zero. (See \setcounter.)