\documentclass{article,report,book or letter}

\documentclass{article,report,book or letter}

A LaTeX document starts with the command 

\documentclass [option] {type}

. The most common document-classes in LaTex are:

book
report
article
letter
All of them are similar, except letter. The main differences can be summerised as follows:

An “article” does not provide “chapter”, whereas “book” and “report” do. Thus, the first structuring element of an “article” is 

\section{name}

.
In a “book”, a header is automatically added to each page indicating the page number as well as the chapter name on even pages and the section name on odd pages
A “book” is always 2-sided whereas in a “report” or “article” you have to specify it by using the “twoside” option. In addition, in a “book” and “report” the “titlepage” and “abstract” will take a whole page each, which is not the
case for “article”. In an “article”, you can use the options “titlepage” and “abstract”.
The “letter” provides a US-type letter format.
Available document structure commands:


Book: 

\part{}, \chapter{}, \section{}, \subsection{}, \subsubsection{}, \paragraph{}, \subparagraph{}

.

Report: 

\part{}, \chapter{}, \section{}, \subsection{}, \subsubsection{}, \paragraph{}, \subparagraph{}

.

Article: 

\part{}, \section{}, \subsection{}, \subsubsection{}, \paragraph{}, \subparagraph{}

.

Letter: A letter does not know the same structuring commands as other formats, but more specific commands like 

\signature{}, \address{}, \opening{} and \closing{}

.

Except 

\part{}

, all structuring commands build a hierarchy. They have a standard formating and numeration.

Other less common document-classes:

“proc” for a protocol (two columns by default and smaller borders on the left and right)
“slides” for a presentations
“minimal, a prototype for your own document type
You can always change the standard document types, by adapting the *.cls-file to your needs.