I know I shouldn't really do this and provide you with the answer without you trying to attempt it first because you won't be learning that way.
But I'm feeling nice today, so I'm providing you of a way of doing a pop up on first load and not loading the pop again until the session been destroyed.
You need to set the session, when you load the page by doing the following:
sessionStorage.setItem('firstVisit', '1');
Then you just need to check for the session like this:
If there is no session called firstVisit
then show message box
if (!sessionStorage.getItem('firstVisit') === "1")
{
$(".message").show();
}
EXAMPLE
HTML
<div class="message">
<div class="message_pad">
<div id="message"></div>
<div class="message_leave">
</div>
</div>
</div>
JavaScript/JQuery
// Save data to sessionStorage
sessionStorage.setItem('firstVisit', '1');
/* Fix size on document ready.*/
$(function()
{
if (!sessionStorage.getItem('firstVisit') === "1")
{
$(".message").show();
}
//Close element.
$(".message").click(function()
{
$(this).hide();
});
$(".message").css({
'height': $(document).height()+'px'
});
$(".message_pad").css({
'left': ($(document).width()/2 - 500/2)+'px'
});
});
/*
* Fix size on resize.
*/
$(window).resize(function(){
$(".message").css({
'height': $(document).height()+'px'
});
$(".message_pad").css({
'left': ($(document).width()/2 - 500/2)+'px'
});
});
JSFIDDLE