Open a Modal Window in SharePoint

Script to open modal popup window.

<script type="text/javascript">

function openDialogWindow()
{

var options =
{

width: 800,
height: 600,
url: 'your url',
title: "Sample Title"
};

SP.UI.ModalDialog.showModalDialog(options);

 </script>

 <a href="#" onclick="javascript:openDialogWindow();">Click Me</a>