How to arrage multiple figures?

The subcaption is useful for this type of thing- it has lots of options. For this particular case, the subfigure environment is useful

Here's a complete MWE to play with

% arara: pdflatex
% !arara: indent: {overwrite: on}
\documentclass{article}
\usepackage{graphicx}
\usepackage{subcaption}

\begin{document}
\begin{figure}[htb]
    \centering
    \begin{subfigure}{.25\textwidth}
        \includegraphics[width=\textwidth]{flower}
        \caption{}
        \label{fig:1flower}
    \end{subfigure}

    \begin{subfigure}{\textwidth}
        \centering
        \includegraphics[width=.5\textwidth]{flower}%
        \includegraphics[width=.5\textwidth]{flower}\\
        \includegraphics[width=.75\textwidth]{flower}
        \caption{}
        \label{fig:3flower}
    \end{subfigure}
    \caption{\ref{fig:1flower}: $1$ flower; \ref{fig:3flower}: $3$ flowers}
\end{figure}
\end{document}

A solution with subfig

\documentclass{article}
\usepackage{subfig}
\usepackage{graphicx}

\newcommand{\subsubfloat}[2]{%
  \begin{tabular}{@{}c@{}}#1\\#2\end{tabular}%
}

\begin{document}

\begin{figure}
\centering
\subfloat[Just One Duck]{\label{duck1}\includegraphics[width=0.3\columnwidth]{duck}}

\subfloat[Three Ducks]{\label{duck2}%
  \begin{minipage}{\columnwidth}\footnotesize
  \centering
  \subsubfloat{\includegraphics[width=0.15\columnwidth]{duck}}{First Duck}%
  \qquad
  \subsubfloat{\includegraphics[width=0.15\columnwidth]{duck}}{Second Duck}

  \medskip

  \subsubfloat{\includegraphics[width=0.3\columnwidth]{duck}}{Third Duck}
  \end{minipage}}

\caption{Four Ducks}
\end{figure}
\end{document}

A solution with subcaption

\documentclass{article}
\usepackage{subcaption}
\usepackage{graphicx}

\newcommand{\subsubfloat}[2]{%
  \begin{tabular}{@{}c@{}}#1\\#2\end{tabular}%
}

\begin{document}

\begin{figure}
\centering
\begin{subfigure}{.3\columnwidth}
\includegraphics[width=\textwidth]{duck}
\caption{Just One Duck}\label{duck1}
\end{subfigure}

\begin{subfigure}{\columnwidth}
  \begin{minipage}{\textwidth}\footnotesize
  \centering
  \subsubfloat{\includegraphics[width=0.15\textwidth]{duck}}{First Duck}%
  \qquad
  \subsubfloat{\includegraphics[width=0.15\textwidth]{duck}}{Second Duck}

  \medskip

  \subsubfloat{\includegraphics[width=0.3\textwidth]{duck}}{Third Duck}
  \end{minipage}
\caption{Three Ducks}\label{duck2}
\end{subfigure}

\caption{Four Ducks}
\end{figure}
\end{document}