can anyone tell me, how to add content below the header, i mean below the red box http://www.elegantthemes.com/preview/eGallery/
Put the code like below in above <div id="container"> <div id="your new css rule"> your content </div>
You need to know some HTML if you want to edit or customize any Wordpress themes. How did you think it was done?
Everyone is telling you the same thing. You need to learn some HTML. There is no "wordrpess code". Worpdress is written in PHP, HTML, and CSS.