Show popup with message

I have site with Umbraco 4.9.0. My task is to show popup with message when user visits some pages for the first time in session.
How could I do it? I am a .Net developer and doesn’t know anything much about Umbraco, except of the fact it is CMS and has been written on ASP.NET MVC.
And couldn’t even find documentation for Umbraco 4.


This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/71033-show-popup-with-message