Packages are files with the extension .sty that either define new commands or redefine existing commands[What are LaTeX classes and packages?]. They're like a type of add-on or plug-in. Most of the commonly used packages should have been installed when you installed your TeX distribution (see §3. From Source Code to Typeset Output). Appendix A. Downloading and Installing Packages covers how to install new packages. Most packages come with documentation that can be accessed using the texdoc application described in §1.1. Class and Package Documentation.
Any applicable class options are also passed to packages, so in
You can specify more than one package in the argument of
\usepackage, where each package name is separated by a
comma. For example:
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