\documentclass{beamer}
\usetheme{Warsaw}
\usepackage{graphicx}
\begin{document}
\title{Beamer Tutorial}
\institute{University of Ioannina}
\date{\today}
\begin{frame}
\maketitle
\end{frame}


\begin{frame}
\frametitle{Outline}
\tableofcontents[part=1,pausesections]
\begin{enumerate}
\item Introduction
\end{enumerate}
\end{frame}

\begin{frame}
\frametitle{Intoduction}
\part{Introduction}
This is the introduction frame.
\end{frame}

\begin{frame}
\frametitle{Overlay - example}
\begin{itemsize}
\item Item 1
\pause
\item Item 2
\pause
\item Item 3
\end{itemize}
\end{frame}


\begin{frame}
\frametitle{Columns example}
\begin{columns}
\column{0.5\textwidth}
This is column 1
\column{0.5\textwidth}
This is column 2
\end{columns}
\end{frame}

\begin{frame}
\frametitle{Items example}
\begin{itemize}
\item <1> First item
\begin{itemize}
  \item Firts subitem
  \item 2nd subitem
\end{itemize}
\item <2> Second item
\end{itemize}
\end{frame}
 
\end{document}