This article is about LaTeX commands. Commands begin with a backslash, followed by the command name, then optional parameters enclosed in square brackets, and required parameters enclosed in curly braces. Commands control the way LaTeX operates, unlike symbols, which render text.
Preamble commands[]
The structure of a LaTeX document is
\documentclass{class}
… your preamble goes here …
\begin{document}
… the text of the document itself goes here …
\end{document}
documentclass command[]
documentclass is the first command of a LaTeX document, and identifies the type of document contained in the input file.
\documentclass{documentclass}
usepackage command[]
usepackage tells LaTeX to load packages of environments, commands, and symbols for specific purposes. The amsmath package, for example, contains a comprehensive set of mathematical symbols.
\usepackage{amssymb,amsmath}
numberwithin command[]
The preamble command, \numberwithin{equation}{section} can be used to number equations with the two-level name m.n (section number.equation number).
input command[]
\input{filename.tex} includes the contents of another file within the current file.
Environment commands[]
An environment exists in the text between the \begin and \end commands.
\begin{environment}
... commands and symbols valid in this environment
\end{environment}