I am in the process of making a website. I have five navigational buttons on the home page. I want to have an overlay with an image appear that states to the affect " must buy product to get access to website". When visitor clicks on any of the navigational buttons initially. Only after visitor pays for the product I am offering, will the overlay go away to give access to navigational buttons to navigate on the website. What programing language do I need to know to be able to set this procedure up? Can you suggest a book I can read to learn How to do this?