\usepackage command\usepackage loads a LaTeX package. Its syntax is similar to
that of LaTeX's \usepackage command:
\usepackage[options]{packages}[version]
where options is a comma-separated list of package
options, packages is a comma-separated list of packages to load
(without the .sty suffix), and version is a package
version number given as a date in the format `YYYY/MM/DD'. If an
older version of the package is found, a warning is issued. If
several packages are loaded within a single \usepackage
command, the options will be applied to each of the packages.
As usual, parameters in square brackets are optional and can be
omitted (together with the square brackets).
For example:
\usepackage[foo,bar]{pack1,pack2}[2005/08/29]
will load packages `pack1' and `pack2', each with the options `foo' and `bar', and will check that each of the packages are dated 2005/08/29 or newer.