The installation is finished, it was really childish. :)
The documentation is a suit of mini video tutorial to understand how to use the plugin, if you need any other help or don't understand how it works, email me, I'll be happy to give you an answer !
TO READ BEFORE ASKING QUESTION
If your theme use a specific template for comment that doesn't use the default fields, go to your file comment.php and put this line
where you want to see your new fields.
The custom commentary field option works only with Themes using the default function :
Codex Wordpress - http://codex.wordpress.org/
Smashing Tutorial - http://www.smashingmagazine.com/
List of all Wordpress hooks - http://adambrown.info/p/wp_hooks/hook
Thanks to the envato team for their help, Greg from Screenfeed.fr for his advices , and Andre Navare for his time spend to test this plugins and for the Video preview.