WordPress Page Restrict

You can check for if a user is logged in or not by is_user_logged_in() if logged in then show the page if not then redirect them. Perfect hook to use for this template_redirect.

Example

function check_and_redirect(){

   if( is_page( 45 ) && !is_user_logged_in() ) {
    wp_redirect( wp_login_url() );
    exit();
    }

}
add_action('template_redirect', 'check_and_redirect');

is_page() is used to check for specific pages, you can use page title, slug.