I want to know the module through which any user can add his own tags for the content on the pages I want to know the module from D7 which i can use to add tags for the any content.
Suppose i have one page Guide for beginners
then on this page there is word "Guide"
So at the bottom of the page there should be Add tag option in which i can add the tag for the word "Guide".
once i tagged it should display at the bottom in my tags.
So this facility should be for any user.
Please let me know the module if any available or the method for implementing this.

Thanks in advance.
Looks like you need to know how to use the Taxonomy module, which comes with Drupal core.

Good place to start would be its documentation.