Then you make the banner on your main page, index.php, and when the user clicks your banner, you can have a text link appear with JavaScript that says "Continue to my site. Click here." but which only shows up after the user clicked on your banner. This is done very simply with JavaScript, I'm not going to tell you exactly how because I don't know the exact environment it's in and I'd rather see someone like you learn JavaScript. It's a useful language if you run a website.
