4 Classes

Document classes  

The document class sets up the general layout of the document, for example:

They can also add new control sequences.

Usage

\documentclass[options]{class-name}

Base classes  

article
for short documents without chapters;
report
for longer documents with chapters, typically single-sided with an abstract;
book
for books, typically double-sided with front matter and back matter;
letter
for correspondence;
slides
for presentations.

Modern classes  

KOMA-Script
scrartcl, scrreprt and scrbook to replace article, report and book, respectively;
memoir
replaces book and report;
beamer
for slides (used to create the course material).

KOMA-Script Example  

\documentclass{scrreprt}  
 
\title{A Sample Document}  
\author{Ann Author}  
 
\begin{document}  
\maketitle  
\tableofcontents  
 
\chapter{Introduction}  
 
This is a sample document with some dummy  
text\footnote{and a footnote}.  
 
\end{document}

Documentation  

On your computer

The texdoc application will show documentation for material you have installed. From the Command Prompt/Terminal

texdoc name

Online

Try CTAN:

http://ctan.org/pkg/name

or texdoc online

http://texdoc.net/pkg/name