what's tags feature for?

I don't understand, what's tags for? what different between tags in Flexicontent and meta keyword.

the tag give an importance for number of utilisation
if you have 100 articles with toto tags you can use tag cloud to help user to discover your article
(sorry my english is to bad ...)
see it on right of this sit
maia31.gouv.fr/
regards

you may think about "tags" as virtual categories.
with tags in cloud or in links on bottom of articles you provide list of linked articles to your users.

for example, you read articles about "how i can use flexicontent" on someone blog. you read all text and want to know, is there another articles about flexicontent on this blog? if author use system of tags on blog you can hit on "flexicontent" world in "tags" section and see list of all articles with "flexicontent" tag.
useful?
i think - yes. so i use it on my own blog in this way

OK, thanks for answer.
This tags is the same as meta tag keywords of Joomla! but not to type every time when i write new article. Tags of Flexicentent is the main tags that I can choose by click. am I right?

short answer:
- meta description and keywords for search optimization
- tag for navigation

so the best solution is set unique keywords for each articles but tags for same articles may be the same