how to add in a page the list of tag used inall the blog

Hey
The easiest way I know of is to create a custom page template. It’s really easy, just follow these steps:
1 – open up your index.php, or single.php
2 – Copy the contents into a new file, save it as tag_archive.php
3 – At the top of that file, paste the following:

<?php
/*
Template Name: Tag Archives
*/
?>

4 – Look for where it says <?php the_content();?> or similar. Replace it with this:

<?php the_content();?>
<ul>
<?php wp_tag_cloud('smallest=8&largest=22&number=0&orderby=name'); ?>
</ul>

5- Save and upload into your themes dir.
6 – Make a new page, and call it tag archives or something. Make a header, and some content, and scroll to the bottom of the page, where the option ‘post template’ is. Click on that, and select dropdown box, going for ‘Tag Archive’.
7 – Publish

Now when you visit your page, you’ll get the title, content and below it, a tag cloud.
Hope this helps!