How to create submenus

Hello...I'trying to add submenus to my main menu, and still didn't suceed. Here's piece of my code in the tag :

body{
background:#eee;color:#000;font-size:11px;font-family:Verdana,sans-serif;margin:0;padding:0;text-align:center}
#tudo{background:#fff;border:#000 1px solid;width:750px;margin:auto;padding:0;text-align:left}
#cabecalho{background:#ccc;font-size:18px;text-align:center;padding:30px}
#menu{background:#000;height:27px;margin:0;padding:0}
#menu ul{margin:0;padding:0;margin-left:6px}

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