Hi,
Best is to add meta info to the individual articles.
http://docs.joomla.org/Making_your_site_Search_Engine_Friendly
<blockquote>
Even though Joomla has a global field for Meta Description (Global Configuration > Site > Global Site Meta Description), you should in most cases leave this blank. Google (and possibly other search engines as well) does not like duplicate title or meta description tags. If you add something to the global field, it will be duplicated on all pages that do not have a specific meta description.</blockquote>
In edenite 2.5 demo the meta info is added in the global plus the article too.
http://easycaptures.com/fs/uploaded/514/8757536653.png
Try changing the same in the article and it should reflect. As advised in the joomla docs, you can leave the global meta info blank.
Regards
Arvind