**
begin{document}
Text here.
begin{figure}
    centering
    begin{subfigure}[!h]{0.3textwidth}
        includegraphics[width=textwidth]{graph01.png}
        caption{A tree.}
    end{subfigure}
~
    begin{subfigure}[!h]{0.3textwidth}
        includegraphics[width=textwidth]{graph02.png}
        caption{Petersen's graph}
    end{subfigure}
    caption{Examples of a graph}
end{figure}
Text here again.
end{document}