A “Tweet This” is an idea to add a link on your blog that web users can simple click to discuss the post on Twiter.com. If you like to add “Tweet This” link into your blog post then add this code in the loop:
<a href=”http://twitter.com/home?status=Currently reading <?php
the_permalink(); ?>” title=”Click to send this page to Twitter!”
Generally, web users wants to display tweet this option at with post header like post author name, published date or at the bottom of the page. Accordingly you will have to add the code in loop of index.php file.