Live Demo

Sounds like you might want a light box,and since you didnt tag your question with jQuery included is a pure JS example of how to make one.

JS

var opener = document.getElementById("opener");

opener.onclick = function(){

    var lightbox = document.getElementById("lightbox"),
        dimmer = document.createElement("div");

    dimmer.style.width =  window.innerWidth + 'px';
    dimmer.style.height = window.innerHeight + 'px';
    dimmer.className = 'dimmer';

    dimmer.onclick = function(){
        document.body.removeChild(this);   
        lightbox.style.visibility = 'hidden';
    }

    document.body.appendChild(dimmer);

    lightbox.style.visibility = 'visible';
    lightbox.style.top = window.innerHeight/2 - 50 + 'px';
    lightbox.style.left = window.innerWidth/2 - 100 + 'px';
    return false;
}

Markup

<div id="lightbox">Testing out the lightbox</div>
<a href="#" id="opener">Click me</a>

CSS

#lightbox{
    visibility:hidden;
    position:absolute;
    background:red;
    border:2px solid #3c3c3c;
    color:white;
    z-index:100;
    width: 200px;
    height:100px;
    padding:20px;
}

.dimmer{
    background: #000;
    position: absolute;
    opacity: .5;
    top: 0;
    z-index:99;
}