Your input file must contain the following commands as a minimum...
\documentstyle{style}
\begin{document}
... your text goes here ...
\end{document}
...where the style selected is one the valid styles for LaTeX.
See section Document Styles, and also see section Overview of LaTeX and Local Guide, for details of the
various document styles available locally.
You may include other LaTeX commands between the \documentstyle
and the \begin{document} commands.