\documentclass{article}

\usepackage{graphicx,subcaption}

\begin{document}

\begin{figure}
  \centering
  \subcaptionbox{First}{\includegraphics[width=.3\linewidth]{example-image-a}} \quad
  \subcaptionbox{Second}{\includegraphics[width=.3\linewidth]{example-image-b}} \quad
  \subcaptionbox{Third}{\includegraphics[width=.3\linewidth]{example-image-c}}
  \caption{Top figure}

  \vspace{2em}

  \subcaptionbox{Fourth}{\includegraphics[width=.3\linewidth]{example-image-c}} \quad
  \subcaptionbox{Fifth}{\includegraphics[width=.3\linewidth]{example-image-b}} \quad
  \subcaptionbox{Sixth}{\includegraphics[width=.3\linewidth]{example-image-a}}
  \caption{Bottom figure}
\end{figure}

\end{document}