User Permission to a Certain Page
It is correct that Drupal has only a very course access control structure for individual nodes (the basic access control system in Drupal is by content type).  For more fine-grained access control than content type, you need to add a node access control module to your site.

There is a page at the Drupal.org wiki giving an overview of node access modules.  You may start by reading that and try to find a suitable module. This page also provides a gentle introduction to node access control in Drupal.

One of these modules is Nodeaccess (also suggested by Ursula).  It lets you control node access (i.e. view, edit, delete) by user and by role.

A simpler alternative is a module named Flexi access.  This only let you set up lists of users (Access Control Lists) that indicate type of access (i.e. view, edit, delete) these users shall have.  It may be simpler to set up and use than Nodeaccess if you don't need to control access by role.

Disclosure: I am a co-maintainer of Flexi access.