Section headings are input as in LaTeX. The output is similar, with a few extra features.
Four levels of headings are provided in REVTeX :
\section{#1}, \subsection{#1}, \subsubsection{#1}, and
\paragraph{#1}. Use the star form of the command to suppress the
automatic numbering; e.g.,
\section*{Introduction}
To label a section heading for cross referencing use the \label{#1}
command after the heading; e.g.,
\section{Introduction}
\label{sec:intro}
All text in the \section{#1} command is automatically set uppercase.
If a lowercase letter is needed, just use \lowercase{x}. For
example, to use ``He'' for helium in a \section{#1} command, type
H\lowercase{e} in #1.
The \appendix command signals that all following sections are
appendixes, so \section{#1} after \appendix will set
#1 as an appendix heading. #1 may be empty. If only one
appendix is used, use a \section*{#1} command to suppress the
appendix letter in the section heading.
Use \protect\\ to force a line break in a section heading. (Fragile
commands must be protected in section headings and captions, and \\
is a fragile command.)
Note: For Physical Review Letters, if there are to be section
headings, use only the fourth-level type, \paragraph{#1}. Use the
``star form'' of the command (\paragraph*{#1}) to avoid the
numbering that is normally attached [(a), (b), 
].