\part, \chapter,
\section, \subsection, \subsubsection,
\paragraph, and \subparagraph.
\part is only used when the separate papers are put together
into one document.
By default,
\part, \chapter, \section, and \subsection
are numbered and placed in the table of contents.
The commands
\setcounter{secnumdepth}{2} % number section and subsections
\setcounter{tocdepth}{2} % and put them in the table of contents
found in the style file may be copied and changed by the editor if desired,
but should not be changed by the individual authors.
The important words in a section argument should be capitalized.