How can you show description of a post in short?

To add  excerpt to a post, 

 1.Simply go to screen option of a post and select excerpt.

 2.Call the following function to show the description in short.

  Syntax:

  When using the excerpt feature WordPress does not automatically provide a link to a page containing the full post. To generate a link include the following   code in the loop directly below: 

      Read More...

           OR

  Put the following in your theme's functions.php:

      function excerpt_read_more_link($output) 

          {

            global $post;

            return $output . ' Read More...';

          }

     add_filter('the_excerpt', 'excerpt_read_more_link');