Individual account access control
Drupal has only a very course access control structure for viewing content.  For the uthenticated use role, you can set permission to 'access content' (Drupal 6) or 'view published content' (Drupal 7), but that's about it.

For more fine-grained access control, you need a node access control module.  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.

One particular module, named Flexi access, allows you to create access control lists consisting of a single user.  This may be what you're looking for.

Disclosure: I am the maintainer of Flexi access.