Enable Post Thumbnails in WordPress

To do this, you must enable the post thumbnails inside your functions.php file. Paste the code below:

add_theme_support( ‘post-thumbnails’ );

Then simply place the following code inside your loop where you want to display the thumbnail:

<?php the_post_thumbnail(); ?>

For More Details : http://www.youtube.com/watch?v=fUfgmRCPI0E#t=147

Enable Post Thumbnails in WordPress