It's a good solution.
But could you help me to change it a little bit. For example using report style in text I wrote:
\documentclass{report}
\usepackage{tocloft,calc}
\renewcommand\chaptername{Introduction}
\renewcommand\cftchappresnum{\chaptername\space}
\setlength{\cftchapnumwidth}{2cm}
\renewcommand{\thechapter}{}
\renewcommand{\thesection}%
{\Roman{section}.}
\pagenumbering{roman}
\renewcommand\chaptername{Introduction}
\chapter{Les initiatives}
\section{Bla bla bla1}
\section{Bla bla bla2}
\clearpage
\pagenumbering{arabic}
\setcounter{chapter}{0} \setcounter{section}{0}
\renewcommand{\chaptername}{Chapter}
\chapter{Les décisions}
Could you please tell me how to make the table of content like this:
Preface..................................i
Introduction. Les initiatives ............v
I.Bla bla bla1..........................vi
II.Bla bla bla2.........................vii
Chapitre 1. Les décisions ................1
1.1 Bla bla bla3 ........................6
1.2 Bla bla bla4 ........................7
Chapitre 2. Les conférence ...............10
Conclusion ...............................30
Appendix A ...............................35
Bibliographie ............................40
The code from answer above works fine, but it needs some changes for me, and I can't handle it well. Thank you.