\documentclass{article}
\usepackage[utf8]{inputenc}

\title{Example of an Article Class Document}
\author{John Smith}
\date{August 2019}

\usepackage{natbib}
\usepackage{graphicx}

\begin{document}

    \maketitle

    \section{Introduction}
    There is a theory which states that if ever anyone discovers exactly what the
    Universe is for and why it is here, it will instantly disappear and be replaced
    by something even more bizarre and inexplicable. There is another theory which
    states that this has already happened.

    \begin{figure}[h!]
        \centering
        \includegraphics[scale=1.7]{universe}
        \caption{The Universe}
        \label{fig:universe}
    \end{figure}

    \section{Conclusion}
    ``I always thought something was fundamentally wrong with the universe''
    \citep{adams1995hitchhiker}

    \bibliographystyle{plain}
    \bibliography{references}
\end{document}
