Latex Presentation: letting bullets appear

You can use \beamerdefaultoverlayspecification.

\documentclass{beamer}
\beamerdefaultoverlayspecification{<+->}
\begin{document}
\begin{frame}
\begin{itemize}
\item A thing.
\item Another thing.
\item And another thing.
\end{itemize}
\end{frame}
\end{document}

There are lots of ways to control this type of effect; it's probably best to consult the relevant sections of the beamer package documentation for more details.

Or you can specify how show each item:

\documentclass{beamer}
\usetheme{Darmstadt}
\begin{document}
\begin{frame}{Only one frame}
\begin{enumerate}
\item<1-> One bullet
\item<3> One more  bullet
\item<2-> Another  bullet   
\end{enumerate}
\end{frame}
\end{document}