private pages or nog

I am using external software to manage newsletter subscriptions. On the site I have a form, once people subscribe they need to be forwarded to a page that is explaining them they are getting an email they need to confirm. I thought that making this page private was the solution, it is when you are logged in as admin but not for others. At the end of the procedure people get on a page where they can download an ebook, after payment, this page also should not be reachable like that. How can I do this??