Subfigures in LaTeX

subfigures.tex

\documentclass{article}

\usepackage{graphicx}
\usepackage{caption}
\usepackage{subcaption}

\begin{document}

\begin{figure}
	\centering
	\begin{subfigure}{0.4\textwidth} % width of left subfigure
		\includegraphics[width=\textwidth]{rncalt.png}
		\caption{RNC} % subcaption
	\end{subfigure}
	\vspace{1em} % here you can insert horizontal or vertical space
	\begin{subfigure}{0.4\textwidth} % width of right subfigure
		\includegraphics[width=\textwidth]{dncalt.png}
		\caption{DNC} % subcaption
	\end{subfigure}
	\caption{Wordcloud of national conventions} % caption for whole figure
\end{figure}

\end{document}

This code not works to me, but this one works => https://tex.stackexchange.com/questions/165728/latex-figure-numbering-as-part-a-b-c