Set a page to be only viewed by users who are logged in
It sounds like you're looking for a node access module. There are many of these modules available which approach this problem in different ways. But in the end, they all allow you to specify more fine grained access rights to nodes (and other types of content). There's a good overview of the various node access modules on drupal.org. This page explains what you should consider when choosing a node access module and describes quite a few of the popular ones. If none of these quite meet your needs and you're up for creating your own custom module check out the documentation for Node Access Rights (here's the Drupal 6 version just in case).



Edit:

In response to the comment from OP, in general you can't set access (view) permissions per content type (though you can set create/edit/delete permissions per content type). So either people can't see any content until they sign in, or they can see all content all the time. So if you have a specific content type that should only ever be visible by logged in users you'll likely need a node access module.