\begin{thebibliography}{widest-label}
\bibitem[label]{cite_key}
.
.
.
\end{thebibliography}
The thebibliography environment produces a bibliography or
reference list. In the article class, this reference list is
labelled "References"; in the report class, it is labelled
"Bibliography".
widest-label: Text that, when printed, is approximately as wide
as the widest item label produces by the \bibitem commands.