documentclass{article}
usepackage[demo]{graphicx}
usepackage{subcaption}
egin{document}
egin{figure}
egin{subfigure}{.5 extwidth}
centering
includegraphics[width=.8linewidth]{image1}
caption{1a}
label{fig:sfig1}
end{subfigure}%
egin{subfigure}{.5 extwidth}
centering
includegraphics[width=.8linewidth]{image2}
caption{1b}
label{fig:sfig2}
end{subfigure}
caption{plots of....}
label{fig:fig}
end{figure}
end{document}