from http://www.emerson.emory.edu/services/latex/latex_132.html
Sectioning commands provide the means to structure your text into units.
\part \chapter (report style only) \section \subsection \subsubsection \paragraph \subparagraph \subsubparagraph (milstd and book-form styles only) \subsubsubparagraph (milstd and book-form styles only)
\part -1 -----> school \chapter 0 ------> semester \section 1 ------> course \subsection 2 -------> HWs \subsubsection 3 ----> HW1,2,3.... \paragraph 4 --------> part(a),(b),..... \subparagraph 5