Original “Twenty Tweleve” theme does not have a search box at top right corner (same row with header).

Here are the steps taken to add a search box:

1. add a folder for child theme in same directory of parent theme, e.g. “/wp-content/themes”
2. name the folder as “twentytwelve-child-theme”
3. refer to http://zeaks.org/create-a-wordpress-child-theme/ on how to create a child theme
   • all modifications are done on child theme rather on parent theme
   • child theme copies/inherits all properties from parent theme
   • copy “header.php” from parent theme, “twentytwelve” to child theme folder, “twentytwelve-child-theme”
   • modify the “header.php” in “twentytwelve-child-theme”
   • modify the “style.css” in “twentytwelve-child-theme”
4. in the “Dashboard -> Appearance -> Themes”, choose the newly created child theme:
   • 

     finally, a search box has been added:
     

Source: http://zeaks.org/tutorials/twenty-twelve-theme-search-form-in-header/