\documentclass[final,letterpaper,twoside,12pt]{article}
\begin{document}
This is a citation of a very~{\cite{c:dummy}} important work.

\begin{thebibliography}{99}
%the '99' allows you up to 99 different references. 
\bibitem{c:dummy} Author, etc.
\end{thebibliography}

\end{document}