How to make "outline" frame in Beamer?

You can do this using \AtBeginSection:

\documentclass{beamer}
\usetheme{Boadilla}

\AtBeginSection[]
{
  \begin{frame}<beamer>
    \frametitle{Outline for section \thesection}
    \tableofcontents[currentsection]
  \end{frame}
}


\begin{document}

\section{Test section one}
\begin{frame} Test \end{frame}
\begin{frame} Test \end{frame}
\section{Test section two}
\begin{frame} Test \end{frame}
\begin{frame} Test \end{frame}

\end{document}

Here's the frame obtained just before the frames for section two: