Adding extra tabs to horizontal navigation bar

Hi i’m newbie using wordpress, currently using raindrops theme developing my new blog. Raindrops is using
<?php
wp_nav_menu( array( 'container_class' => 'menu-header', 'theme_location' => 'primary'));
?>
to generate the horizontal navigation bar with only 1 tab linked to posts->category being displayed,
i wish i can add more tabs such as faq, contact us etc.which can be linked to wherever i want to,
how can it be done> Thanks alot.