\documentclass[12pt]{article}
\author {vasiliki faloutsou}
\title {my first section}
\begin {document}
\maketitle
\section {my first section}
\par my first paragraph
\subsection {my first subsection}
\begin{center}
       ''Latex is a document preparation system and document Latex is not the name of a particular editing programm refers to the encoding or tagging conventions 
\end{center}
\end{document}       
