Two figures side by side

%% thanks to https://tex.stackexchange.com/a/5770

\begin{figure}
    \centering
    \begin{minipage}{0.45\textwidth}
        \centering
        \includegraphics[width=0.9\textwidth]{example-image-a} % first figure itself
        \caption{first figure}
    \end{minipage}\hfill
    \begin{minipage}{0.45\textwidth}
        \centering
        \includegraphics[width=0.9\textwidth]{example-image-b} % second figure itself
        \caption{second figure}
    \end{minipage}
\end{figure}