\usepackage: Additional packages ¶To load a package pkg, with the package options given in the comma-separated list options:
\usepackage[options]{pkg}[mindate]
To specify more than one package you can separate them with a comma,
as in \usepackage{pkg1,pkg2,...}, or use multiple
\usepackage commands.
If the mindate optional argument is given, LaTeX gives a
warning if the loaded package has an earlier date, i.e., is too old.
The mindate argument must be in the form YYYY/MM/DD.
More info on this: https://tex.stackexchange.com/questions/47743.
\usepackage must be used in the document preamble, between the
\documentclass declaration and the \begin{document}.
Occasionally it is necessary to load packages before the
\documentclass; see \RequirePackage for that
(see \RequirePackage).
Any options given in the global \documentclass command that are
unknown to the selected document class are passed on to the packages
loaded with \usepackage.