I think you are French, so I would suggest you to read the eZ publish doc that you can find in french (not all the doc, but enough to know what you need to begin with eZP):
You can override pagelayout.tpl for class 'article' and remove a part of template code (with {menu name=LeftMenu} and change {$maincontentstyle} in <div id="maincontent" class="{$maincontentstyle}">
or in your original pagelayout.tpl add code
{if $module_result.content_info.class_identifier|eq('article')}
do without leftmenu
{else}
with leftmenu
{/if}