Hi I read in this time Drupal cms. I want know that how can create a horizontal menu(header menu)

By default, Drupal outputs a menu as unordered list (<ul>). In your theme, you can use css to display this list horizontal. If you want to learn about theming, read the documentation on this site. Also have a look at http://themegarden.org where you can see a lot of Drupal themes. See what you like and then look at the code to see how they did it.