Edit in JSFiddle

$('.open').click(function() {
    $("#panel").animate({
        width: 'toggle'
    }, 300);
});

#panel
{
     height: 600px;
     width: 200px;
    padding:20px;
     background: #eee;
     float: left;
     display: none;    
     color: #666;
     font-size: xx-large;
}
.open
{
     height: 20px;
     width: 70px;
     background: #666;
    padding:20px;
     float: left; 
     margin-top: 200px;
    color:#fff;
}

<div id='panel'>
    Hello
</div>
<div class='open'>
    Open
</div>