Synopsis:
\begin{environment-name}
...
\end{environment-name}
An environment is an area of LaTeX source, inside of which
there is a distinct behavior. For instance, for poetry in LaTeX
put the lines between \begin{verse} and \end{verse}.
\begin{verse}
There once was a man from Nantucket \\
...
\end{verse}
See Environments, for a list of environments. Particularly notable is
that every LaTeX document must have a document environment,
a \begin{document} ... \end{document} pair.
The environment-name at the beginning must exactly match that at
the end. This includes the case where environment-name ends in a
star (*); both the \begin and \end texts must
include the star.
Environments may have arguments, including optional arguments. This example produces a table. The first argument is optional (and causes the table to be aligned on its top row) while the second argument is required (it specifies the formatting of columns).
\begin{tabular}[t]{r|l}
... rows-of-table ...
\end{tabular}