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This is a WAY open-ended question. I feel that if you did some research you’d find LOTS of answers. Here’s how I would go about it.

Install or modify your code to use a members only plugin. Lock all the Non-Member pages. I’m confused on what you men by check a banner, but if the banner is just going to a registration page then block that page unless a query string something like example.net/register?banner=true has been set. If they go to example.net/register it would return false.

I’m not sure I answer your question like I said it’s super open-ended. That’s how I would do it. (if I understand the question)

EDIT:

You’ll need to use a PHP $_SESSION or even a $_COOKIE to see if the user clicked the banner. I would do something like this.

Make a category “premium” and assign all preminum page to that category.

Add this to your functions.php in your theme

add_action( 'template_redirect', 'premium_redirect' );

function premium_redirect(){
   //see if post is in category of premium
   if(in_category('premium')){
        //see if the banner variable is set
        $banner_check =$_GET['banner'];
        //set the session (or cookie)
        if($banner_check == 'true'){$_SESSION['banner'] = 'true';}
        ///see if the $banner and the $_SESSION is set if not take them to the banner page
        if($_SESSION['banner'] != 'true'){
                 wp_redirect('http://example.net/bannerpage');
        }
     return;
    } //end cat check
return;
}

then have your banner link to example.net/premiumpage?banner=true

I haven’t tested this but I us similar approaches all the time. You may also need to use a custom post type for pages instead of in_category see http://codex.wordpress.org/Conditional_Tags#A_Post_Type