\documentclass[12pt]{article}

\begin{document}
 
 Citations can be made using the {\tt cite} command. You can have citations to a single \cite{Swe15}
 or multiple \cite{BKW+13,DWL02,Swe15} references.

\nocite{*}

\bibliographystyle{plain}

\bibliography{example8a}

\end{document}