\documentclass{article}
\usepackage{geometry}
\usepackage{fancyhdr}
\usepackage{amsmath,amsthm,amssymb}
\usepackage{graphicx}
\usepackage{hyperref}
\usepackage{lipsum}

\begin{document}
This is some preamble text that you enter yourself.

\section{Text for the first section}
\lipsum[1]

\subsection{Text for a subsection of the first section}
\lipsum[2-3]

\subsection{Another subsection of the first section}
\lipsum[4-5]

\section{The second section}
\lipsum[6]

\subsection{Title of the first subsection of the second section}
\lipsum[7]
\end{document}